{"id":13494,"date":"2026-05-15T00:00:00","date_gmt":"2026-05-15T00:00:00","guid":{"rendered":"https:\/\/www.mailgun.com\/blog\/quel-port-smtp-comprendre-les-ports-25-465-587\/"},"modified":"2026-05-16T03:49:41","modified_gmt":"2026-05-16T03:49:41","slug":"quel-port-smtp-comprendre-les-ports-25-465-587","status":"publish","type":"blog","link":"https:\/\/www.mailgun.com\/fr\/blog\/email\/quel-port-smtp-comprendre-les-ports-25-465-587\/","title":{"rendered":"Quel port SMTP utiliser\u00a0? Comprendre les ports 25, 465 &amp; 587"},"content":{"rendered":"\n<p>It&rsquo;s a common question that we receive here at Sinch Mailgun about <b>SMTP port numbers<\/b>. To ensure connectivity to our Simple Mail Transfer Protocol (SMTP) endpoint, Mailgun offers <a href=\"https:\/\/www.mailgun.com\/fr\/products\/send\/smtp\/\" target=\"_tabs\" rel=\"noopener noreferrer\">multiple SMTP port options<\/a>, but which one should you use to send email messages? We\u2019ll take a historical look at each SMTP port and then we&rsquo;ll discuss today&rsquo;s methodology for outgoing mail usage. If you&rsquo;re not a history buff, go to \u00ab\u00a0Today&rsquo;s Usage\u00a0\u00bb for the most common SMTP ports.<\/p>\n\r\n    <nav data-content-type=\"longform\" class=\"toc-block longform-spacings px-5 py-6 px-md-6 px-lg-7 py-md-7 bg-light fs-sm rounded-lg\" aria-labelledby=\"toc-title-6584\"><p class=\"h5 m-0\" id=\"toc-title-6584\">Table of contents<\/p><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">01<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#what-is-smtp\">What is SMTP?<\/a><a class=\"scrollme link-body-color\" href=\"#what-is-smtps\">What is SMTPS?<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">02<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#what-is-an-smtp-port\">What is an SMTP port?<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">03<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#what-different-smtp-ports-are-there-understanding-ports-25-465-587\">What different SMTP ports are there? Understanding ports 25, 465, 587<\/a><a class=\"scrollme link-body-color\" href=\"#port-25-the-standard-port\">Port 25: The standard port<\/a><a class=\"scrollme link-body-color\" href=\"#port-587-the-default-port\">Port 587: The default port<\/a><a class=\"scrollme link-body-color\" href=\"#port-465-the-tls-port\">Port 465: The TLS port<\/a><a class=\"scrollme link-body-color\" href=\"#port-2525-the-alternative-port\">Port 2525: The alternative port<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">04<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#what-smtp-port-should-you-use\">What SMTP port should you use?<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">05<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#why-is-it-important-to-use-the-right-smtp-port\">Why is it important to use the right SMTP port?<\/a><a class=\"scrollme link-body-color\" href=\"#smtp-ports-and-email-security\">SMTP ports and email security<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">06<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#understanding-smtp-vs-smtps-security-differences\">Understanding SMTP vs SMTPS: Security differences\u00a0<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">07<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#understanding-smtps-and-end-to-end-email-encryption-differences\">Understanding SMTPS and end-to-end email encryption differences<\/a><a class=\"scrollme link-body-color\" href=\"#smtp-ports-and-email-deliverability\">SMTP ports and email deliverability<\/a><a class=\"scrollme link-body-color\" href=\"#common-smtp-port-issues-and-solutions\">Common SMTP port issues and solutions\u00a0<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">08<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#what-are-pop-and-imap-protocols\">What are POP and IMAP protocols?<\/a><\/div><\/div><div class=\"d-flex mt-3\"><div class=\"w-auto fw-bold text-accent d-flex me-2\">09<\/div><div class=\"d-flex flex-column\"><a class=\"fw-bold scrollme link-body-color text-accent\" href=\"#using-smtp-with-mailgun\">Using SMTP with Mailgun<\/a><\/div><\/div><\/nav>    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-primary\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> <b>Quick SMTP port reference guide:<\/b><\/div><ul class=\"mb-0 mt-3\"><li>Port 25: Standard SMTP port for server-to-server email relay (often blocked for high spam use)<\/li><li>Port 587: Default secure port for email submission (recommended)<\/li><li>Port 465: Legacy SMTPS port (use only if required)<\/li><li>Port 2525: Alternative port when others are blocked<\/li><\/ul>\r\n    <\/div>\r\n\n<h2 class=\"wp-block-heading\">What is SMTP?<\/h2>\n\n<p><b>SMTP stands for Simple Mail Transfer Protocol <\/b>\u2013 put simply, it\u2019s the process by which <a href=\"https:\/\/www.mailgun.com\/fr\/products\/send\/smtp\/free-smtp-service\/free-open-smtp-relay\/\" target=\"_tabs\" rel=\"noopener noreferrer\">emails are sent across the internet<\/a>. Message data is sent out and the traffic is directed into ports. Once message data travels successfully through a port, other email authentications are used to validate the messages and either deliver them to the inbox, reject them, or direct them to the spam folder.<\/p>\n\n<h3 class=\"wp-block-heading\">What is SMTPS?<\/h3>\n\n<p>SMTPS is more secure than SMTP in the same way that HTTPS is more secure than HTTP. In the earlier days of the internet <a href=\"http:\/\/www.http\" target=\"_tabs\" rel=\"noopener noreferrer\">www.http<\/a> was the standard beginning to an email address. But it became easy for spammers and spoofers to intercept sensitive data. HTTPS = HTTP + SSL, or secure socket layer, which is an internet address\u2019s extra layer of authentication. SMTPS is SMTP + <a href=\"https:\/\/www.mailgun.com\/fr\/resources\/learn\/glossary\/transport-layer-security\/\" target=\"_tabs\" rel=\"noopener noreferrer\">TLS, or transport layer security<\/a>, which uses encryption and authentication to further protect SMTP.<\/p>\n\n<p><b>TLS uses a digital signature to verify the origin of traffic.<\/b> In email we talk a lot about authentication to verify a senders <i>identity<\/i> with protocols like SPF or DKIM. <a href=\"https:\/\/www.mailgun.com\/blog\/deliverability\/email-authentication-your-id-card-sending\/\" target=\"_tabs\" rel=\"noopener noreferrer\">Instead of verifying who sends a message<\/a>, TLS verifies by <i>where<\/i> email traffic comes from. If the origin in the signature matches the actual origin, the data is allowed through. The default SMTP port for SMTPS is port 587, but more on that in a bit. Before we talk about default ports, we first have to know what an SMTP port is.<\/p>\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> If you\u2019re a sender with Sinch Mailgun you can use SMTPS by enabling TLS on your mail server. <a href='https:\/\/documentation.mailgun.com\/docs\/mailgun\/user-manual\/smtp-protocol\/#smtp-relay'>Learn more.<\/a><\/div>\r\n    <\/div>\r\n\n<h2 class=\"wp-block-heading\">What is an SMTP port?<\/h2>\n\n<p>Ports are endpoints that individual servers use to connect to a network and retrieve data. Think of it like an old school switchboard with a technician plugging the incoming call into a jack to connect it to a specific phone.<b> An SMTP port is<\/b>\u00a0 <b>a port designed to direct email <\/b><b><i>through<\/i><\/b><b> a network to its recipient.<\/b><\/p>\n\n<p>The most important SMTP ports are:<\/p>\n\n<ul class=\"wp-block-list\">\n<li>Port 25<\/li>\n\n\n\n<li>Port 587<\/li>\n\n\n\n<li>Port 465<\/li>\n<\/ul>\n\n<p>The thing is, not all SMTP ports are equal. Choosing the wrong one could have negative consequences and reflect poorly on you as a sender.<\/p>\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" class=\"wp-image-4088\" width=\"1024\" height=\"260\" src=\"https:\/\/www.mailgun.com\/wp-content\/uploads\/2025\/07\/SMTP-or-API-Email-Sending__1_.png\" alt=\"How SMTP works\" srcset=\"https:\/\/www.mailgun.com\/wp-content\/uploads\/2025\/07\/SMTP-or-API-Email-Sending__1_.png 1024w, https:\/\/www.mailgun.com\/wp-content\/uploads\/2025\/07\/SMTP-or-API-Email-Sending__1_-300x76.png 300w, https:\/\/www.mailgun.com\/wp-content\/uploads\/2025\/07\/SMTP-or-API-Email-Sending__1_-768x195.png 768w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n<h2 class=\"wp-block-heading\">What different SMTP ports are there? Understanding ports 25, 465, 587<\/h2>\n\n<p>There are many ports to choose from, but only a few that you might want to use. Like with anything technical, where we started is not where we are now. When the SMTP protocol was first published in 1981 (the same year Lionel Richie\u2019s <i>Endless Love<\/i> topped the charts \u2013 for perspective) it didn\u2019t take long before the first port, port 25 was put into place to manage message traffic.<\/p>\n\n<p>What about the rest of the SMTP ports? How many other ports were launched over time and have they evolved? Many have, and some have even been depricated. When it comes to ports, there are many. Here\u2019s our breakdown \u2013 or \u201cport reduction\u201d if you will. Sorry, we couldn\u2019t resist.<\/p>\n\n<h3 class=\"wp-block-heading\">Port 25: The standard port<\/h3>\n\n<p>The first port,<b> port 25<\/b>, was implemented as the primary message transmission channel to help mitigate against attacks like man-in-the-middle. It came out of a 1982 request from the University of Southernn California to the Internet Engineering Task Force (IETF) who are the overlords of all protocols that control movement across the internet.<\/p>\n\n<p>Ironically, SMTP port 25 has since become favored by spammers because of its support for open relay.<\/p>\n\n<p>SMTP port 25 continues to be used primarily for SMTP relaying. SMTP relaying is the transmission of email from email server to email server.<\/p>\n\n<p><b>In most cases, modern SMTP email clients (Microsoft Outlook, Mail, Thunderbird, etc.) shouldn&rsquo;t use this port. It is traditionally blocked by residential ISPs and Cloud Hosting Providers, to curb the amount of spam that is relayed from compromised computers or servers. <\/b>Unless you&rsquo;re specifically managing a mail server, you should have no traffic traversing this port on your computer or server.<\/p>\n\n<h3 class=\"wp-block-heading\">Port 587: The default port<\/h3>\n\n<p>In December of 1998, after port 25 started to get spammy, R. Gellens and J. Klensin submitted RFC <a href=\"http:\/\/tools.ietf.org\/html\/rfc2476\" target=\"_tabs\" rel=\"noopener noreferrer\">2476<\/a> in support of adding a new specification for internet email communications. The RFC proposed a split of the traditional message submission and message relay concept.<\/p>\n\n<p>The RFC defined that message submission should occur over port 587 to ensure new policy and security requirements don&rsquo;t interfere with the traditional relay traffic over message relay port 25.<\/p>\n\n<p><a href=\"https:\/\/www.mailgun.com\/blog\/deliverability\/smtp-port-587\/\" target=\"_tabs\" rel=\"noopener noreferrer\"><b>Port 587 is the default mail submission port.<\/b><\/a> When an email client or outgoing server is submitting an email to be routed by a proper mail server, it should always use SMTP port 587 as the default port.<\/p>\n\n<p>This port, coupled with TLS encryption, will ensure that email is submitted securely and following the guidelines set out by the IETF.<\/p>\n\n<p>All Mailgun Send customers should consider using port 587 as their default SMTP port unless you&rsquo;re explicitly blocked by your upstream network or hosting provider.<\/p>\n\n<h3 class=\"wp-block-heading\">Port 465: The TLS port<\/h3>\n\n<p><a href=\"https:\/\/www.iana.org\/\" target=\"_tabs\" rel=\"noopener noreferrer\">The Internet Assigned Numbers Authority (IANA)<\/a><i> has reassigned a<\/i><a href=\"http:\/\/www.iana.org\/assignments\/service-names-port-numbers\/service-names-port-numbers.txt\" target=\"_tabs\" rel=\"noopener noreferrer\"> new service<\/a><i> to this port, and it should no longer be used for SMTP communications.<\/i><\/p>\n\n<p>Because port 465 was once recognized by IANA as valid, there may be legacy systems that are only capable of using this connection method. Typically, you will use this port only if your application demands it. A quick Google search, and you&rsquo;ll find many consumer Inbox Service Providers&rsquo; (ISPs) articles that suggest port 465 as the recommended setup. However, we do not recommend it, as it is not RFC compliant.<\/p>\n\n<p><b>Interestingly, port 465 was never published as an official SMTP transmission or submission channel by the IETF<\/b>. Instead, the Internet Assigned Numbers Authority (IANA), which maintains much of the core internet infrastructure, registered port 465 for SMTPS. The purpose was to establish a port for SMTP to operate using Secure Sockets Layer (SSL). SSL is commonly used for encrypting communications over the internet.<\/p>\n\n<p>The port was assigned for about one year before it was revoked in support of securing SMTP communications using Transport Layer Security (TLS). The nail in the coffin was a new protocol command \u00ab\u00a0STARTTLS,\u00a0\u00bb introduced in RFC<a href=\"http:\/\/tools.ietf.org\/html\/rfc2487\" target=\"_tabs\" rel=\"noopener noreferrer\"> 2487<\/a>. This command allows SMTP servers to communicate over existing ports by advertising whether the destination server supports TLS encryption. If so, the sending server can upgrade the connection using the \u00ab\u00a0STARTTLS\u00a0\u00bb SMTP command.<\/p>\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> In addition to many port options, there are also many SMTP commands. Learn more in our post on <a href='https:\/\/www.mailgun.com\/blog\/deliverability\/smtp-commands\/'>SMTP commands.<\/a><\/div>\r\n    <\/div>\r\n\n<p><b>Mailgun supports TLS connections, which you can verify by connecting and issuing an \u00ab\u00a0ehlo\u00a0\u00bb from a command line interface. <\/b>The resultant \u00ab\u00a0250 STARTTLS\u00a0\u00bb confirms the endpoint accepts TLS connection requests.<\/p>\n    <div data-content-type=\"longform\" class=\"code-snippet longform-spacings rounded-lg overflow-hidden shadow \" data-count=\"1\">\r\n        <ul class=\"nav nav-buttons code-snippet__tabs longform-except position-relative d-flex gap-2 flex-wrap p-3\" role=\"tablist\">\r\n\r\n                            \r\n                    \r\n                        <li class=\"nav-item\" role=\"presentation\">\r\n                            <button class=\"nav-link active\" data-bs-toggle=\"tab\" data-bs-target=\"#code_0\" type=\"button\" role=\"tab\" aria-controls=\"code_0\" aria-selected=\"true\">\r\n                                PHP                            <\/button>\r\n                        <\/li>\r\n\r\n                    \r\n                            \r\n        <\/ul>\r\n        <div class=\"code-snippet__tab-content tab-content overflow-hidden\">\r\n\r\n                            \r\n                    <div class=\"tab-pane show active\" id=\"code_0\" role=\"tabpanel\" aria-labelledby=\"code_0\">\r\n                        <pre class=\"w-100 h-100 m-0 line-numbers language-PHP\">\r\n                            <code class=\"language-PHP\">\r\n\r\n                                &gt; telnet smtp.mailgun.org 587rnTrying 50.56.21.178...  rnConnected to smtp.mailgun.org.  rnEscape character is &#039;^]&#039;.  rn220 ak47 ESMTP ready  rn&gt; ehlo blog.mailgun.comrn250-ak47  rn250-AUTH PLAIN LOGIN  rn250-SIZE 52428800  rn250-8BITMIME  rn250-ENHANCEDSTATUSCODES  rn250 STARTTLS  \r\n                            <\/code>\r\n                        <\/pre>\r\n                    <\/div>\r\n                                    <\/div>\r\n    <\/div>\r\n\n<p>You can test using the same command sequence on any SMTP server. Try Gmail or Yahoo, \u00ab\u00a0telnet gmail-smtp-in.l.google.com 25\u00a0\u00bb or \u00ab\u00a0telnet mta7.am0.yahoodns.net 25\u00a0\u00bb.<\/p>\n\r\n    <aside data-content-type=\"longform\"  class=\"banner-block longform-spacings rounded-lg shadow-lg px-5 py-6 px-md-6 py-md-7 p-lg-7 bg-light\" data-theme=\"dark\" aria-labelledby=\"banner-block-block_a5fb3ba2ab131a3577be25564193b8eb\">\r\n                    <p class=\"text-uppercase section-caption text-body-color\">\r\n                Learn about our Deliverability Services            <\/p>\r\n                            <p class=\"h4 text-accent fw-bold\" id=\"banner-block-block_a5fb3ba2ab131a3577be25564193b8eb\">\r\n                Deliverability Services            <\/p>\r\n                            <div class=\"mb-0 text-body-color\">\r\n                                    <div class=\"content-body mb-0 text-body-color\">Looking to send a high volume of emails? Our email experts can supercharge your email performance. See how we&#x27;ve helped companies like Lyft, Shopify, Github increase their email delivery rates to an average of 97%.<\/div>\r\n                            <\/div>\r\n        \r\n        <div class=\"text-start mt-5\"><a href=\"https:\/\/www.mailgun.com\/fr\/solutions\/service-delivrabilite-email\/\"  class=\"btn btn-secondary\" >Learn more<\/a><\/div>\r\n    <\/aside>\r\n\r\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> Both ports 587 and 465 support TLS, port 465 is used for implicit TLS but port 587 which uses startTLS is preferred because message communications aren\u2019t restricted by clients that don\u2019t support encryption.<\/div>\r\n    <\/div>\r\n\n<h3 class=\"wp-block-heading\">Port 2525: The alternative port<\/h3>\n\n<p><b>This port is not endorsed by the IETF nor IANA.<\/b> Instead, Mailgun provides it as an alternate port, which mirrors port 587, in the event the above ports are blocked. Because 2525 is a non-traditional high port number, it is typically allowed on consumer ISPs and Cloud Hosting providers, like Google Compute Engine. If you\u2019ve tried the above ports, but experience connectivity issues, try port 2525. This port also supports TLS encryption.<\/p>\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> There are several SMTP ports but not all are created equal. The most frequently used is port 25 for SMTP relays, while port 587 is the default port for mail submission<!-- -->.<\/div>\r\n    <\/div>\r\n\n<h2 class=\"wp-block-heading\">What SMTP port should you use?<\/h2>\n\n<p>When you start talking about protocols, you know the specifics are going to matter. SMTP is no different. Your port depends on what type of sender you are.<\/p>\n\n<p><b>Most used ports:<\/b><\/p>\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Port<\/th><th>Use case\u00ad<\/th><\/tr><\/thead><tbody><tr><td>Port\u00ad 25: The stan\u00addard port\u00ad<\/td><td>\n<strong>Us\u00ade for non-\u00adencrypted conn\u00adections.<\/strong> Stil\u00adl thou\u00adght of as the stan\u00addard SMTP\u00ad port\u00ad, most\u00ad resi\u00addential  ISPs\u00ad and host\u00ading prov\u00adiders bloc\u00adk port\u00ad 25 due to heav\u00ady spam\u00ad traf\u00adfic.\n<\/td><\/tr><tr><td>Port\u00ad 465:\u00ad The TLS port\u00ad<\/td><td>\n<strong>Us\u00ade if your\u00ad appl\u00adication or comp\u00adany requ\u00adire.<\/strong> Port\u00ad 465 is a port\u00ad that\u00ad carr\u00adies out mess\u00adage subm\u00adission over\u00ad Impl\u00adicit TLS prot\u00adocol.\n<\/td><\/tr><tr><td>Port\u00ad 587:\u00ad The defa\u00adult port\u00ad<\/td><td><strong>Us\u00ade for your\u00ad busi\u00adness or for secu\u00adre conn\u00adections.<\/strong> Port\u00ad 587 is the defa\u00adult SMTP\u00ad port\u00ad, most\u00ad busi\u00adnesses use this\u00ad port\u00ad.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n<p><b>Alternative ports:<\/b><\/p>\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Port<\/th><th>Use case\u00ad<\/th><\/tr><\/thead><tbody><tr><td>Port\u00ad 80: The HTTP\u00ad port\u00ad<\/td><td><strong>Us\u00ade as the defa\u00adult port\u00ad for unen\u00adcrypted webp\u00adages.<\/strong> Port\u00ad 80 is used\u00ad to send\u00ad and rece\u00adive web-\u00adbased comm\u00adunications and HTML\u00ad data\u00ad and allo\u00adws HTML\u00ad data\u00ad to rema\u00adin in plai\u00adn text\u00ad, vs. Port\u00ad 443 wher\u00ade it woul\u00add be encr\u00adypted.<\/td><\/tr><tr><td>Port\u00ad 443:\u00ad The SSL port\u00ad<\/td><td>\n<strong>Us\u00ade to get to an HTTP\u00adS addr\u00adess.<\/strong> When\u00ad you send\u00ad a mess\u00adage, SMTP\u00ad tran\u00adsmits mess\u00adages to a spec\u00adific addr\u00adess for proc\u00adessing. Port\u00ad 80 is use to open\u00ad an HTTP\u00ad addr\u00adess, port\u00ad 443 is used\u00ad for HTTP\u00adS, or addr\u00adesses that\u00ad have\u00ad SSL secu\u00adrity. (The\u00ad \u2018s\u2019 in HTTP\u00adS)\n<\/td><\/tr><tr><td>Port\u00ad 588:\u00ad The seco\u00adndary emai\u00adl port\u00ad<\/td><td>\n<strong>Us\u00ade if you requ\u00adire TLS encr\u00adyption.<\/strong> Both\u00ad port\u00ads 587 and 588 can be coup\u00adled with\u00ad TLS encr\u00adyption for add data\u00ad priv\u00adacy and secu\u00adrity.\n<\/td><\/tr><tr><td>Port\u00ad 2525\u00ad: The alte\u00adrnate port\u00ad<\/td><td>\n<strong>Us\u00ade as an alte\u00adrnate if port\u00ad 587 is bloc\u00adked.<\/strong> Mail\u00adgun prov\u00adides an alte\u00adrnate in port\u00ad 2525\u00ad for situ\u00adations when\u00ad stan\u00addard port\u00ads are bloc\u00adked. Most\u00ad ESPs\u00ad supp\u00adort port\u00ad 2525\u00ad.\n<\/td><\/tr><\/tbody><\/table><\/figure>\n\n<h2 class=\"wp-block-heading\">Why is it important to use the right SMTP port?<\/h2>\n\n<p>Using the right port helps ensure delivery and supports your sender reputation. But watch out, some ports have evolved to have a bad reputation of their own \u2013 and using these ports could keep you out of the inbox.<\/p>\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> Choosing the wrong SMTP port could negatively impact your deliverability and sender reputation.\u00a0<\/div>\r\n    <\/div>\r\n\n<h3 class=\"wp-block-heading\">SMTP ports and email security<\/h3>\n\n<p>Different ports are associated with different security measures, so choosing the right one is key to ensure you\u2019re protecting your email communications.<\/p>\n\n<p>Some ports transmit encrypted messages, while other ports remain open for all types of traffic. The port you use may be determined by the security standards of your organization or by the sensitive contents of the messages you send.<\/p>\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Port<\/th><th>Best\u00ad For<\/th><th>Secu\u00adrit\u00ady<\/th><th>Reco\u00admmended Use Case\u00ad<\/th><\/tr><\/thead><tbody><tr><td>25<\/td><td>Serv\u00ader rela\u00ady<\/td><td>Basi\u00adc<\/td><td>Lega\u00adcy syst\u00adems only\u00ad<\/td><\/tr><tr><td>587<\/td><td>Mess\u00adage subm\u00adission<\/td><td>TLS supp\u00adort<\/td><td>Mode\u00adrn emai\u00adl send\u00ading<\/td><\/tr><tr><td>465<\/td><td>Lega\u00adcy syst\u00adems<\/td><td>Impl\u00adicit TLS<\/td><td>When\u00ad spec\u00adifically requ\u00adired<\/td><\/tr><tr><td>2525<\/td><td>Alte\u00adrnative opti\u00adon<\/td><td>TLS supp\u00adort<\/td><td>When\u00ad othe\u00adr port\u00ads are bloc\u00adked<\/td><\/tr><\/tbody><\/table><\/figure>\n\n<h2 class=\"wp-block-heading\">Understanding SMTP vs SMTPS: Security differences\u00a0<\/h2>\n\n<p>If you\u2019re looking into SMTP, chances are you\u2019re going to come across SMTPS. SMTPS is more secure than SMTP in the same way that HTTPS is more secure than HTTP. In the earlier days of the internet, <a href=\"http:\/\/www.http\/\" target=\"_tabs\" rel=\"noopener noreferrer\"><u>www.http<\/u><\/a> was the standard beginning to an email address. But it became easy for spammers and spoofers to intercept sensitive data.<\/p>\n\n<p>In our table above we break down the basic security protocols and primary uses of SMTP ports, but let\u2019s dig a little deeper in what makes these ports secure and why you should avoid some.<\/p>\n\n<ul class=\"wp-block-list\">\n<li><b>Port 25<\/b>: Used for SMTP relay between mail servers. Frequently blocked by ISPs to prevent spam abuse, making it insecure for client email submission. Not recommended for outbound email sending.<\/li>\n\n\n\n<li><b>Port 587<\/b>: The standard for secure email submission with STARTTLS encryption. Ensures authentication and prevents unauthorized access, reducing the risk of credential theft and spam abuse.<\/li>\n\n\n\n<li><b>Port 465<\/b>: Historically assigned for SMTPS (implicit TLS) but deprecated. Some legacy systems still use it, but modern security protocols favor STARTTLS on port 587 for better flexibility and encryption negotiation.<\/li>\n\n\n\n<li><b>Port 2525<\/b>: An alternative port provided by some services to bypass restrictions. It functions similarly to port 587 with support for TLS and is useful as a fallback option when standard ports are blocked, maintaining secure transmission standards.<\/li>\n<\/ul>\n\n<h2 class=\"wp-block-heading\">Understanding SMTPS and end-to-end email encryption differences<\/h2>\n\n<p><b>How does SMTPS differ from end-to-end email encryption?<\/b>SMTPS encrypts emails during their transmission across servers but does not provide end-to-end encryption. End-to-end encryption methods like PGP or S\/MIME ensure that only the sender and recipient can access the email content, providing a higher level of security.<\/p>\n\n<p>How SMTPS enhances security<\/p>\n\n<ul class=\"wp-block-list\">\n<li>HTTPS = HTTP + SSL (Secure Socket Layer)<\/li>\n\n\n\n<li>SMTPS = SMTP + TLS (Transport Layer Security)<\/li>\n\n\n\n<li>Uses encryption and authentication<\/li>\n\n\n\n<li>Protects against data interception<\/li>\n<\/ul>\n\n<h3 class=\"wp-block-heading\">SMTP ports and email deliverability<\/h3>\n\n<p>Choosing the right SMTP port also helps ensure you have strong deliverability. SMTP is the most used protocol by mail servers to communicate, but that doesn\u2019t mean they\u2019re interchangeable. Some ISPs may block certain ports, like port 25 to defend against spam, and default to another port, like port 587 that supports encryption. <\/p>\n\n<p>Adding authentication protocols like SMTP AUTH can help improve your message delivery, but <a href=\"https:\/\/www.mailgun.com\/blog\/email\/understanding-email-deliverability\/\" target=\"_tabs\" rel=\"noopener noreferrer\">deliverability<\/a> is a multi-ingredient pie. Everything from your message content to your authentication <a href=\"https:\/\/www.mailgun.com\/blog\/deliverability\/deliverability-impacts-roi\/\" target=\"_tabs\" rel=\"noopener noreferrer\">can impact your sender reputation<\/a> and overall deliverability rate.<\/p>\n\n<p>In order to determine which port is the best for you, let\u2019s cover the most popular ports and the traffic they transmit.<\/p>\n\n<h3 class=\"wp-block-heading\">Common SMTP port issues and solutions\u00a0<\/h3>\n\n<h4 class=\"wp-block-heading\">Connection Timeouts\u00a0<\/h4>\n\n<p>When your email client can&rsquo;t establish a connection to the SMTP server within the expected timeframe. This often occurs due to network issues, firewall restrictions, or when the server is experiencing high load.\u00a0<\/p>\n\n<ul class=\"wp-block-list\">\n<li>Check your network connectivity and try increasing the timeout setting in your email client\u00a0<\/li>\n\n\n\n<li>Verify firewall rules aren&rsquo;t blocking SMTP traffic and test on a different network if possible\u00a0<\/li>\n<\/ul>\n\n<h4 class=\"wp-block-heading\">Authentication Failures<\/h4>\n\n<p>These happen when the credentials provided (username\/password) don&rsquo;t match what the SMTP server expects, or when using the wrong authentication method. Most commonly occurs after password changes or when using outdated credentials.\u00a0<\/p>\n\n<ul class=\"wp-block-list\">\n<li>Double-check your SMTP username and password are correct and regenerate API keys if needed\u00a0<\/li>\n\n\n\n<li>Ensure you&rsquo;re using the correct authentication method (PLAIN, LOGIN, or CRAM-MD5) required by your SMTP server\u00a0<\/li>\n<\/ul>\n\n<h4 class=\"wp-block-heading\">Port Blocking<\/h4>\n\n<p>ISPs or firewalls may block specific SMTP ports, especially port 25, as a spam prevention measure. If you&rsquo;re experiencing connection issues, try switching to port 587 or 2525 as alternatives.\u00a0<\/p>\n\n<ul class=\"wp-block-list\">\n<li>Try port 587 first as it&rsquo;s the modern standard for secure email submission\u00a0<\/li>\n\n\n\n<li>If port 587 is blocked, use port 2525 as Mailgun&rsquo;s alternative port with identical functionality\u00a0<\/li>\n<\/ul>\n\n<h4 class=\"wp-block-heading\">TLS Negotiation Issues<\/h4>\n\n<p>Problems occur when there&rsquo;s a mismatch between the TLS versions supported by your client and the SMTP server, or when certificates are invalid or expired. Usually resolved by updating your TLS configuration or ensuring proper certificate management.\u00a0<\/p>\n\n<ul class=\"wp-block-list\">\n<li>Update your client to support modern TLS versions (TLS 1.2 or higher recommended)\u00a0<\/li>\n\n\n\n<li>Check your server&rsquo;s SSL\/TLS certificates are valid and not expired in your configuration\u00a0<\/li>\n<\/ul>\n\n<h2 class=\"wp-block-heading\">What are POP and IMAP protocols?<\/h2>\n\n<p>POP (Post Office Protocol, with the latest version being POP3) and IMAP (Internet Message Access Protocol) are two of the <a href=\"https:\/\/www.mailgun.com\/blog\/email\/imap-vs-pop\/\" target=\"_tabs\" rel=\"noopener noreferrer\">very first protocols developed<\/a> on the consumer internet that allowed for email clients &#8211; like Outlook, Thunderbird and others &#8211; to retrieve mail from a mail server.<\/p>\n\n<p>The ports typically used for POP are TCP ports 110 and 995, and for IMAP are TCP ports 143 and 993, for insecure and secure sessions respectively. They were each good at doing different things, like reflecting the state of an email back to the server (whether it was read, flagged, or marked as junk), or for preserving a copy of the message on a local machine for easy offline access.\u00a0 The latest version of POP, POP3, can be used with or without SMTP. <\/p>\n    <div data-content-type=\"longform\"  class=\"callout text-body-color px-5 py-6 px-md-6 px-lg-7 py-md-7 longform-spacings rounded-lg bg-light\" data-theme=\"light\">\r\n\r\n        <div class=\"content-body\"> This does not affect which port you can use with Mailgun Send. Mailgun doesn\u2019t host mailboxes, so these aren\u2019t protocols we support. Learn more about Pop vs IMAP<a href='https:\/\/www.mailgun.com\/blog\/email\/imap-vs-pop\/'> in our post on the difference between these protocols<\/a>.\u00a0<\/div>\r\n    <\/div>\r\n\n<h2 class=\"wp-block-heading\">Using SMTP with Mailgun<\/h2>\n\n<p><a href=\"https:\/\/www.mailgun.com\/fr\/fonctionnalites\/serveur-smtp\/\" target=\"_tabs\" rel=\"noopener noreferrer\">SMTP<\/a> has been around for years, and many folks ask us whether they should use SMTP or <a href=\"https:\/\/www.mailgun.com\/fr\/fonctionnalites\/email-api\/\" target=\"_tabs\" rel=\"noopener noreferrer\">Mailgun&rsquo;s API endpoint<\/a>. Deciding whether you should <a href=\"https:\/\/www.mailgun.com\/blog\/email\/when-should-you-use-email-api\/\" target=\"_tabs\" rel=\"noopener noreferrer\">use an email API<\/a> or SMTP to send your emails might not be an easy choice.<\/p>\n\n<p>We certainly recognize there is some level of vendor lock-in associated with building around an API. However, SMTP is extremely \u00ab\u00a0chatty\u00a0\u00bb and may lead to less performant mail submission to Mailgun.<\/p>\n\n<p>For example, consider the typical TLS mail conversation between my computer and Mailgun&rsquo;s SMTP endpoint:<\/p>\n    <div data-content-type=\"longform\" class=\"code-snippet longform-spacings rounded-lg overflow-hidden shadow \" data-count=\"1\">\r\n        <ul class=\"nav nav-buttons code-snippet__tabs longform-except position-relative d-flex gap-2 flex-wrap p-3\" role=\"tablist\">\r\n\r\n                            \r\n                    \r\n                        <li class=\"nav-item\" role=\"presentation\">\r\n                            <button class=\"nav-link active\" data-bs-toggle=\"tab\" data-bs-target=\"#code_0\" type=\"button\" role=\"tab\" aria-controls=\"code_0\" aria-selected=\"true\">\r\n                                PHP                            <\/button>\r\n                        <\/li>\r\n\r\n                    \r\n                            \r\n        <\/ul>\r\n        <div class=\"code-snippet__tab-content tab-content overflow-hidden\">\r\n\r\n                            \r\n                    <div class=\"tab-pane show active\" id=\"code_0\" role=\"tabpanel\" aria-labelledby=\"code_0\">\r\n                        <pre class=\"w-100 h-100 m-0 line-numbers language-PHP\">\r\n                            <code class=\"language-PHP\">\r\n\r\n                                &gt; openssl s_client -starttls smtp -crlf -connect smtp.mailgun.org:587rn250 STARTTLS  rn&gt; ehlo blog.mailgun.comrn250-ak47  rn250-AUTH PLAIN LOGIN  rn250-SIZE 52428800  rn250-8BITMIME  rn250-ENHANCEDSTATUSCODES  rn&gt; AUTH PLAIN AHBvc3RtYXN0ZXJAc2FtcGxlcy5tYWlsZ3VuLm9yZwAza2g5dW11am9yYTU=rn235 2.0.0 OK  rn&gt; MAIL FROM:&lt;test@samples.mailgun.org&gt;rn250 Sender address accepted  rn&gt; RCPT TO:&lt;recipient@samples.mailgun.org&gt;rn250 Recipient address accepted  rn&gt; DATArn354 Continue  rn&gt; This is a test of SMTP over port 587.rn&gt; .rn250 Great success  rn&gt; QUITrn221 See you later. Yours truly, Mailgun  \r\n                            <\/code>\r\n                        <\/pre>\r\n                    <\/div>\r\n                                    <\/div>\r\n    <\/div>\r\n\n<p>As you can see, the above communication is quite cumbersome with lots of back and forth between sender and receiver. We open a connection to the SMTP server, issue the EHLO command, authenticate, set the MAIL FROM, set the RCPT TO, DATA command, send the data, period to close, and finally receive confirmation the message was queued.<\/p>\n\n<p>Compare this with an HTTPs payload:<\/p>\n    <div data-content-type=\"longform\" class=\"code-snippet longform-spacings rounded-lg overflow-hidden shadow \" data-count=\"1\">\r\n        <ul class=\"nav nav-buttons code-snippet__tabs longform-except position-relative d-flex gap-2 flex-wrap p-3\" role=\"tablist\">\r\n\r\n                            \r\n                    \r\n                        <li class=\"nav-item\" role=\"presentation\">\r\n                            <button class=\"nav-link active\" data-bs-toggle=\"tab\" data-bs-target=\"#code_0\" type=\"button\" role=\"tab\" aria-controls=\"code_0\" aria-selected=\"true\">\r\n                                PHP                            <\/button>\r\n                        <\/li>\r\n\r\n                    \r\n                            \r\n        <\/ul>\r\n        <div class=\"code-snippet__tab-content tab-content overflow-hidden\">\r\n\r\n                            \r\n                    <div class=\"tab-pane show active\" id=\"code_0\" role=\"tabpanel\" aria-labelledby=\"code_0\">\r\n                        <pre class=\"w-100 h-100 m-0 line-numbers language-PHP\">\r\n                            <code class=\"language-PHP\">\r\n\r\n                                &gt; openssl s_client -connect api.mailgun.net:443rn&gt; POST \/v2\/samples.mailgun.org\/messages HTTP\/1.1rn&gt; Authorization: Basic YXBpOmtleS0zYXg2eG5qcDI5amQ2ZmRzNGdjMzczc2d2anh0ZW9sMA==rn&gt; Content-Type: application\/x-www-form-urlencodedrn&gt; Content-Length: 126rn&gt; rn&gt; from=test%40samples.mailgun.org&amp;to=recipient%40samples.mailgun.org&amp;subject=Testing&amp;rn&gt; text=This+is+a+test+of+HTTP+over+port+443!rnHTTP\/1.1 200 OK  \r\n                            <\/code>\r\n                        <\/pre>\r\n                    <\/div>\r\n                                    <\/div>\r\n    <\/div>\r\n\n<p>Here, we initiate a connection, pass the HTTP POST payload and receive a 200 OK from the API endpoint. We don&rsquo;t have to issue a sequence of commands and wait for a response from the server after each command.<\/p>\n\n<p>To learn more, check out our <a href=\"http:\/\/documentation.mailgun.com\/\" target=\"_tabs\" rel=\"noopener noreferrer\">Documentation<\/a> for more info, or <a href=\"https:\/\/www.mailgun.com\/fr\/contact\/\" target=\"_tabs\" rel=\"noopener noreferrer\">contact us<\/a> and we can answer any questions you may have about SMTP ports or our email services.<\/p>\n\r\n    <aside data-content-type=\"longform\"  class=\"banner-block longform-spacings rounded-lg shadow-lg px-5 py-6 px-md-6 py-md-7 p-lg-7 bg-light\" data-theme=\"dark\" aria-labelledby=\"banner-block-block_1eb4bce52ddfd734f1bf81f71dee8961\">\r\n                    <p class=\"text-uppercase section-caption text-body-color\">\r\n                Sign Up            <\/p>\r\n                            <p class=\"h4 text-accent fw-bold\" id=\"banner-block-block_1eb4bce52ddfd734f1bf81f71dee8961\">\r\n                It&rsquo;s easy to get started. And it&rsquo;s free.            <\/p>\r\n                            <div class=\"mb-0 text-body-color\">\r\n                                    <div class=\"content-body mb-0 text-body-color\">See what you can accomplish with the world\u2019s best email delivery platform.<\/div>\r\n                            <\/div>\r\n        \r\n        <div class=\"text-start mt-5\"><a href=\"https:\/\/signup.mailgun.com\/new\/signup\"  class=\"btn btn-secondary\" >Get started<\/a><\/div>\r\n    <\/aside>\r\n\r\n","protected":false},"excerpt":{"rendered":"<p>It&rsquo;s a common question that we receive here at Sinch Mailgun about SMTP port numbers. To ensure connectivity to our Simple Mail Transfer Protocol (SMTP) endpoint, Mailgun offers multiple SMTP port options, but which one should you use to send email messages? We\u2019ll take a historical look at each SMTP port and then we&rsquo;ll discuss [&hellip;]<\/p>\n","protected":false},"author":13,"featured_media":4074,"menu_order":0,"template":"","meta":{"_acf_changed":true,"footnotes":""},"blog_category":[20],"class_list":["post-13494","blog","type-blog","status-publish","has-post-thumbnail","hentry","blog_category-email"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Quel port SMTP utiliser\u00a0? Comprendre les ports 25, 465 &amp; 587 - Transactional Email API Service For Developers | Mailgun<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.mailgun.com\/fr\/blog\/email\/quel-port-smtp-comprendre-les-ports-25-465-587\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Quel port SMTP utiliser\u00a0? Comprendre les ports 25, 465 &amp; 587 - Transactional Email API Service For Developers | Mailgun\" \/>\n<meta property=\"og:description\" content=\"It&rsquo;s a common question that we receive here at Sinch Mailgun about SMTP port numbers. To ensure connectivity to our Simple Mail Transfer Protocol (SMTP) endpoint, Mailgun offers multiple SMTP port options, but which one should you use to send email messages? We\u2019ll take a historical look at each SMTP port and then we&rsquo;ll discuss [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.mailgun.com\/fr\/blog\/email\/quel-port-smtp-comprendre-les-ports-25-465-587\/\" \/>\n<meta property=\"og:site_name\" content=\"Transactional Email API Service For Developers | Mailgun\" \/>\n<meta property=\"article:modified_time\" content=\"2026-05-16T03:49:41+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.mailgun.com\/wp-content\/uploads\/2025\/07\/MG-Blog-Email.png\" \/>\n\t<meta property=\"og:image:width\" content=\"720\" \/>\n\t<meta property=\"og:image:height\" content=\"448\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"13 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.mailgun.com\\\/fr\\\/blog\\\/email\\\/quel-port-smtp-comprendre-les-ports-25-465-587\\\/\",\"url\":\"https:\\\/\\\/www.mailgun.com\\\/fr\\\/blog\\\/email\\\/quel-port-smtp-comprendre-les-ports-25-465-587\\\/\",\"name\":\"Quel port SMTP utiliser\u00a0? 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Comprendre les ports 25, 465 &amp; 587 - Transactional Email API Service For Developers | Mailgun","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.mailgun.com\/fr\/blog\/email\/quel-port-smtp-comprendre-les-ports-25-465-587\/","og_locale":"fr_FR","og_type":"article","og_title":"Quel port SMTP utiliser\u00a0? Comprendre les ports 25, 465 &amp; 587 - Transactional Email API Service For Developers | Mailgun","og_description":"It&rsquo;s a common question that we receive here at Sinch Mailgun about SMTP port numbers. To ensure connectivity to our Simple Mail Transfer Protocol (SMTP) endpoint, Mailgun offers multiple SMTP port options, but which one should you use to send email messages? 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