{"id":20251,"date":"2026-05-01T00:00:00","date_gmt":"2026-05-01T00:00:00","guid":{"rendered":"https:\/\/www.mailgun.com\/blog\/smtp-fehlercodes\/"},"modified":"2026-09-15T11:53:31","modified_gmt":"2026-09-15T11:53:31","slug":"smtp-fehlercodes","status":"publish","type":"blog","link":"https:\/\/www.mailgun.com\/de\/blog\/email\/smtp-fehlercodes\/","title":{"rendered":"SMTP-Fehlercodes und was sie bedeuten"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Email seems kind of magical, until it breaks. You hit send and expect your message to reach the inbox, but sometimes, it bounces back with a cryptic error message. There are many types of errors since there are many pieces to the email puzzle that make the magic happen. <a href=\"https:\/\/www.mailgun.com\/de\/blog\/deliverability\/email-bounces-was-tun\/\" target=\"_tabs\" rel=\"noopener noreferrer\">Bounce errors<\/a> get brought up quite a bit but what about SMTP errors?<\/p>\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.mailgun.com\/de\/blog\/email\/welchen-smtp-port-verwenden-die-ports-25-465-587-verstehen\/\" target=\"_tabs\" rel=\"noopener noreferrer\">SMTP, or <b>Simple Mail Transfer Protocol<\/b>,<\/a> is the language servers use to talk to each other when sending emails. When something breaks during that conversation, the server returns a code to explain what happened.<\/p>\n\n<p class=\"wp-block-paragraph\">These <b>status codes<\/b> offer valuable insights, helping you figure out what went wrong and how to fix it. From temporary glitches to permanent failures, SMTP codes help you stay on top of your <a href=\"https:\/\/www.mailgun.com\/de\/blog\/deliverability\/deliverability-academy-folge-eins-zusammenfassung\/#chapter-1\" target=\"_tabs\" rel=\"noopener noreferrer\">email delivery.<\/a><\/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-8267\"><p class=\"h5 m-0\" id=\"toc-title-8267\">Inhaltsverzeichnis<\/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=\"#how-smtp-codes-work\">How SMTP codes work<\/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=\"#common-smtp-errors-explained\">Common SMTP errors explained<\/a><a class=\"scrollme link-body-color\" href=\"#temporary-issues\">Temporary issues<\/a><a class=\"scrollme link-body-color\" href=\"#permanent-failures\">Permanent failures<\/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=\"#bonus-enhanced-status-codes\">Bonus: enhanced status codes<\/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=\"#smtp-response-codes-decoded\">SMTP response codes, decoded<\/a><a class=\"scrollme link-body-color\" href=\"#complete-smtp-error-codes-list\">Complete SMTP error codes list<\/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=\"#wrapping-up\">Wrapping up<\/a><\/div><\/div><\/nav>\n<h2 class=\"wp-block-heading\">How SMTP codes work<\/h2>\n\n<p class=\"wp-block-paragraph\">SMTP codes are short \u2013 just three digits \u2013 but packed with meaning.<\/p>\n\n<p class=\"wp-block-paragraph\">The first digit tells you the type of response:<\/p>\n\n<ul class=\"wp-block-list\">\n<li><b>2 means success:<\/b> The requested action was completed.<\/li>\n\n\n\n<li><b>4 signals a temporary problem:<\/b> You can try again later.<\/li>\n\n\n\n<li><b>5 means permanent failure:<\/b> You need to fix something before retrying.<\/li>\n<\/ul>\n\n<p class=\"wp-block-paragraph\">The second and third digits offer more detail, pointing to specific issues like authentication, routing, or mailbox problems.<\/p>\n\n<p class=\"wp-block-paragraph\">Reading SMTP codes is like learning a simple language. Once you get it, troubleshooting gets easier and faster.<\/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\"> Want to know more about SMTP and how it works? If you\u2019re an email geek like us, the answer is yes. Check out our post on <a href=\"https:\/\/www.mailgun.com\/de\/blog\/deliverability\/was-ist-smtp\/\">what is SMTP and how does it work to learn more.<\/a><\/div>\r\n    <\/div>\r\n\n<h2 class=\"wp-block-heading\">Common SMTP errors explained<\/h2>\n\n<p class=\"wp-block-paragraph\">While there are many codes out there, some show up more often. Let\u2019s walk through key types of SMTP responses and what they mean.<\/p>\n\n<h3 class=\"wp-block-heading\">Temporary issues<\/h3>\n\n<p class=\"wp-block-paragraph\">Temporary errors suggest a short-term problem. In most cases, trying again later works. For example, if you see <b>421 service not available<\/b>, the receiving server might be temporarily offline or too busy. A <b>450 mailbox unavailable<\/b> error means the recipient\u2019s inbox is full or temporarily disabled. Timeouts, like <b>447 timeout occurred<\/b>, often point to server or connection issues that should resolve quickly.<\/p>\n\n<h3 class=\"wp-block-heading\">Permanent failures<\/h3>\n\n<p class=\"wp-block-paragraph\">Permanent errors signal that something must be fixed before the email can be sent again.<\/p>\n\n<p class=\"wp-block-paragraph\">A <b>550 mailbox unavailable<\/b> error means the address does not exist. <b>553 mailbox name not allowed<\/b> often indicates a formatting issue or that the domain is rejecting your message. And <b>554 transaction failed<\/b> may mean your message hit a <b>spam filter<\/b> or was blocked by the recipient\u2019s server.<\/p>\n\n<h2 class=\"wp-block-heading\">Bonus: enhanced status codes<\/h2>\n\n<p class=\"wp-block-paragraph\">Some servers use enhanced SMTP codes to provide extra details. These codes, such as <b>5.1.1 bad destination mailbox address<\/b>, are more specific and help zero in on problems like typos or invalid domains.<\/p>\n\n<p class=\"wp-block-paragraph\">Understanding both basic and enhanced codes gives you full visibility into email issues.<\/p>\n\n<h2 class=\"wp-block-heading\">SMTP response codes, decoded<\/h2>\n\n<p class=\"wp-block-paragraph\">At first glance, SMTP errors seem complicated. But with a little guidance, they become clear signals that help you fix issues fast. From syntax mistakes to blocked domains, reading these codes helps keep your email program running smoothly and your messages landing in inboxes.<\/p>\n\n<h3 class=\"wp-block-heading\">Complete SMTP error codes list<\/h3>\n\n<p class=\"wp-block-paragraph\">Here is a list of SMTP error codes you may encounter, and some quick solutions that may help.<\/p>\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\nCode\n<\/th><th>\nWhat\u00ad it mean\u00ads\n<\/th><th>\nHow to fix it\n<\/th><\/tr><\/thead><tbody><tr><td>\n101\n<\/td><td>\nThe conn\u00adection fail\u00aded due to an inva\u00adlid SSL or TLS conf\u00adiguration.\n<\/td><td>\nRevi\u00adew your\u00ad serv\u00ader&#8217;s secu\u00adrity sett\u00adings and veri\u00adfy SSL\/\u00adTLS cert\u00adificates are vali\u00add and corr\u00adectly inst\u00adalled.\n<\/td><\/tr><tr><td>\n111\n<\/td><td>\nThe send\u00ading serv\u00ader was unab\u00adle to conn\u00adect to the remo\u00adte SMTP\u00ad serv\u00ader.\n<\/td><td>\nChec\u00adk the netw\u00adork conn\u00adection, fire\u00adwall rule\u00ads, and ensu\u00adre the reci\u00adpient serv\u00ader is onli\u00adne and acce\u00adpting conn\u00adections.\n<\/td><\/tr><tr><td>\n221\n<\/td><td>\nThe doma\u00adin\u2019s serv\u00ader is clos\u00ading the tran\u00adsmission chan\u00adnel \u2014 this\u00ad usua\u00adlly happ\u00adens afte\u00adr a succ\u00adessful emai\u00adl sess\u00adion.\n<\/td><td>\nNo acti\u00adon need\u00aded. This\u00ad is norm\u00adal when\u00ad comm\u00adunication is comp\u00adlete.\n<\/td><\/tr><tr><td>\n250\n<\/td><td>\nThe requ\u00adested acti\u00adon was comp\u00adleted succ\u00adessfully.\n<\/td><td>\nNo fix requ\u00adired \u2014 this\u00ad mean\u00ads your\u00ad emai\u00adl was acce\u00adpted.\n<\/td><\/tr><tr><td>\n420\n<\/td><td>\nA fire\u00adwall or filt\u00ader bloc\u00adked the emai\u00adl befo\u00adre it coul\u00add be deli\u00advered.\n<\/td><td>\nRevi\u00adew reci\u00adpient poli\u00adcies, spam\u00ad filt\u00aders, and IP repu\u00adtation to ensu\u00adre your\u00ad emai\u00adls are allo\u00adwed thro\u00adugh.\n<\/td><\/tr><tr><td>\n421\n<\/td><td>\nThe reci\u00adpient&#8217;s mail\u00ad serv\u00ader is temp\u00adorarily unav\u00adailable or busy\u00ad.\n<\/td><td>\nWait\u00ad and retr\u00ady late\u00adr. If pers\u00adistent, cont\u00adact the reci\u00adpient&#8217;s serv\u00ader admi\u00adn.\n<\/td><\/tr><tr><td>\n422\n<\/td><td>\nThe reci\u00adpient\u2019s mail\u00adbox has exce\u00adeded its stor\u00adage quot\u00ada.\n<\/td><td>\nAsk the reci\u00adpient to clea\u00adr spac\u00ade or wait\u00ad unti\u00adl they\u00ad reso\u00adlve the issu\u00ade.\n<\/td><\/tr><tr><td>\n431\n<\/td><td>\nTher\u00ade is not enou\u00adgh stor\u00adage or memo\u00adry avai\u00adlable to proc\u00adess the mess\u00adage.\n<\/td><td>\nRetr\u00ady late\u00adr or cont\u00adact the reci\u00adpient serv\u00ader admi\u00adnistrator to reso\u00adlve capa\u00adcity issu\u00ades.\n<\/td><\/tr><tr><td>\n441\n<\/td><td>\nThe conn\u00adection was drop\u00adped befo\u00adre the serv\u00ader coul\u00add fini\u00adsh proc\u00adessing the mess\u00adage.\n<\/td><td>\nChec\u00adk netw\u00adork stab\u00adility and retr\u00ady.\n<\/td><\/tr><tr><td>\n442\n<\/td><td>\nThe serv\u00ader star\u00adted proc\u00adessing the mess\u00adage but the conn\u00adection was unex\u00adpectedly clos\u00aded.\n<\/td><td>\nInve\u00adstigate poss\u00adible netw\u00adork inte\u00adrruptions or serv\u00ader-side time\u00adouts.\n<\/td><\/tr><tr><td>\n446\n<\/td><td>\nThe mess\u00adage has loop\u00aded thro\u00adugh too many\u00ad serv\u00aders and was reje\u00adcted.\n<\/td><td>\nRevi\u00adew mail\u00ad rout\u00ading rule\u00ads and veri\u00adfy corr\u00adect MX reco\u00adrds.\n<\/td><\/tr><tr><td>\n447\n<\/td><td>\nThe send\u00ading serv\u00ader expe\u00adrienced a time\u00adout whil\u00ade wait\u00ading for a resp\u00adonse.\n<\/td><td>\nRetr\u00ady send\u00ading late\u00adr and chec\u00adk for conn\u00adectivity or serv\u00ader load\u00ad issu\u00ades.\n<\/td><\/tr><tr><td>\n449\n<\/td><td>\nA DNS look\u00adup fail\u00aded duri\u00adng the deli\u00advery atte\u00admpt.\n<\/td><td>\nChec\u00adk the reci\u00adpient doma\u00adin\u2019s DNS conf\u00adiguration and retr\u00ady late\u00adr.\n<\/td><\/tr><tr><td>\n450\n<\/td><td>\nThe mail\u00adbox is temp\u00adorarily unav\u00adailable \u2014 ofte\u00adn due to bein\u00adg full \u00ad or inac\u00adtive.\n<\/td><td>\nRetr\u00ady afte\u00adr some\u00ad time\u00ad or veri\u00adfy the reci\u00adpient emai\u00adl addr\u00adess.\n<\/td><\/tr><tr><td>\n451\n<\/td><td>\nThe serv\u00ader enco\u00aduntered a loca\u00adl erro\u00adr whil\u00ade proc\u00adessing the emai\u00adl.\n<\/td><td>\nRetr\u00ady late\u00adr. If pers\u00adistent, cont\u00adact the reci\u00adpient\u2019s emai\u00adl admi\u00adnistrator.\n<\/td><\/tr><tr><td>\n452\n<\/td><td>\nThe rece\u00adiving serv\u00ader does\u00ad not have\u00ad enou\u00adgh stor\u00adage to acce\u00adpt your\u00ad mess\u00adage.\n<\/td><td>\nWait\u00ad and retr\u00ady. For pers\u00adistent issu\u00ades, noti\u00adfy the reci\u00adpient.\n<\/td><\/tr><tr><td>\n454\n<\/td><td>\nTLS encr\u00adyption is requ\u00adired but unav\u00adailable at the mome\u00adnt.\n<\/td><td>\nChec\u00adk your\u00ad serv\u00ader&#8217;s TLS sett\u00adings or retr\u00ady late\u00adr when\u00ad the reci\u00adpient serv\u00ader supp\u00adorts encr\u00adyption.\n<\/td><\/tr><tr><td>\n471\n<\/td><td>\nThe mess\u00adage was bloc\u00adked by an anti\u00ad-spam or fire\u00adwall rule\u00ad.\n<\/td><td>\nChec\u00adk your\u00ad send\u00ading IP and cont\u00adent for spam\u00ad trig\u00adgers and remo\u00adve prob\u00adlematic elem\u00adents.\n<\/td><\/tr><tr><td>\n500\n<\/td><td>\nThe comm\u00adand sent\u00ad was unre\u00adcognized or form\u00adatted inco\u00adrrectly.\n<\/td><td>\nVeri\u00adfy the SMTP\u00ad comm\u00adands and chec\u00adk for typo\u00ads or synt\u00adax erro\u00adrs.\n<\/td><\/tr><tr><td>\n501\n<\/td><td>\nThe para\u00admeters or argu\u00adments prov\u00adided are not vali\u00add.\n<\/td><td>\nRevi\u00adew the reci\u00adpient emai\u00adl addr\u00adess and comm\u00adand synt\u00adax.\n<\/td><\/tr><tr><td>\n502\n<\/td><td>\nThe comm\u00adand used\u00ad is not supp\u00adorted by the rece\u00adiving serv\u00ader.\n<\/td><td>\nRevi\u00adew the prot\u00adocol comp\u00adatibility and avoi\u00add unsu\u00adpported comm\u00adands.\n<\/td><\/tr><tr><td>\n503\n<\/td><td>\nComm\u00adands were\u00ad sent\u00ad out of orde\u00adr or at the wron\u00adg time\u00ad.\n<\/td><td>\nRevi\u00adew the sequ\u00adence of SMTP\u00ad comm\u00adands and adju\u00adst your\u00ad send\u00ading logi\u00adc to foll\u00adow the corr\u00adect orde\u00adr.\n<\/td><\/tr><tr><td>\n504\n<\/td><td>\nThe comm\u00adand para\u00admeter prov\u00adided is not supp\u00adorted by the serv\u00ader.\n<\/td><td>\nRemo\u00adve unsu\u00adpported para\u00admeters or adju\u00adst for comp\u00adatibility with\u00ad the reci\u00adpient serv\u00ader.\n<\/td><\/tr><tr><td>\n510\n<\/td><td>\nThe reci\u00adpient addr\u00adess was inva\u00adlid or inco\u00adrrectly form\u00adatted.\n<\/td><td>\nVeri\u00adfy the emai\u00adl addr\u00adess for typo\u00ads or erro\u00adrs.\n<\/td><\/tr><tr><td>\n511\n<\/td><td>\nThe reci\u00adpient\u2019s mail\u00adbox does\u00ad not exis\u00adt.\n<\/td><td>\nDoub\u00adle-check the reci\u00adpient\u2019s emai\u00adl addr\u00adess or conf\u00adirm with\u00ad them\u00ad dire\u00adctly.\n<\/td><\/tr><tr><td>\n512\n<\/td><td>\nThe doma\u00adin part\u00ad of the reci\u00adpient addr\u00adess does\u00ad not exis\u00adt.\n<\/td><td>\nVeri\u00adfy the doma\u00adin&#8217;s DNS reco\u00adrds or corr\u00adect any typo\u00ads in the emai\u00adl addr\u00adess.\n<\/td><\/tr><tr><td>\n513\n<\/td><td>\nThe serv\u00ader does\u00ad not allo\u00adw rela\u00adying or the addr\u00adess type\u00ad is inco\u00adrrect.\n<\/td><td>\nConf\u00adirm rela\u00adying perm\u00adissions or corr\u00adect the addr\u00adess form\u00adat.\n<\/td><\/tr><tr><td>\n515\n<\/td><td>\nThe dest\u00adination mail\u00adbox addr\u00adess is inva\u00adlid.\n<\/td><td>\nConf\u00adirm the reci\u00adpient\u2019s emai\u00adl addr\u00adess and fix any issu\u00ades.\n<\/td><\/tr><tr><td>\n517\n<\/td><td>\nThe send\u00ader\u2019s mail\u00ad attr\u00adibutes are inco\u00adrrect or unsu\u00adpported.\n<\/td><td>\nRevi\u00adew and corr\u00adect the send\u00ader&#8217;s addr\u00adess and sett\u00adings.\n<\/td><\/tr><tr><td>\n521\n<\/td><td>\nThe reci\u00adpient doma\u00adin does\u00ad not acce\u00adpt inco\u00adming mail\u00ad.\n<\/td><td>\nCont\u00adact the doma\u00adin owne\u00adr or choo\u00adse an alte\u00adrnative cont\u00adact meth\u00adod.\n<\/td><\/tr><tr><td>\n522\n<\/td><td>\nThe reci\u00adpient has exce\u00adeded thei\u00adr mail\u00adbox limi\u00adt.\n<\/td><td>\nAsk the reci\u00adpient to free\u00ad up spac\u00ade or retr\u00ady late\u00adr.\n<\/td><\/tr><tr><td>\n523\n<\/td><td>\nThe emai\u00adl is too larg\u00ade for the rece\u00adiving serv\u00ader to acce\u00adpt.\n<\/td><td>\nRedu\u00adce atta\u00adchment size\u00ad or comp\u00adress the emai\u00adl cont\u00adent and rese\u00adnd.\n<\/td><\/tr><tr><td>\n530\n<\/td><td>\nAuth\u00adentication is requ\u00adired to send\u00ad emai\u00adl to this\u00ad serv\u00ader.\n<\/td><td>\nConf\u00adigure and prov\u00adide vali\u00add SMTP\u00ad auth\u00adentication cred\u00adentials.\n<\/td><\/tr><tr><td>\n531\n<\/td><td>\nThe mail\u00ad syst\u00adem is full\u00ad and cann\u00adot acce\u00adpt more\u00ad mess\u00adages.\n<\/td><td>\nWait\u00ad and retr\u00ady late\u00adr or noti\u00adfy the reci\u00adpient.\n<\/td><\/tr><tr><td>\n533\n<\/td><td>\nThe remo\u00adte serv\u00ader does\u00ad not have\u00ad enou\u00adgh disk\u00ad spac\u00ade to stor\u00ade the emai\u00adl.\n<\/td><td>\nRetr\u00ady late\u00adr or cont\u00adact the reci\u00adpient\u2019s serv\u00ader admi\u00adnistrator.\n<\/td><\/tr><tr><td>\n534\n<\/td><td>\nThe auth\u00adentication mech\u00adanism used\u00ad is too weak\u00ad for this\u00ad serv\u00ader\u2019s poli\u00adcy.\n<\/td><td>\nUpgr\u00adade to a stro\u00adnger auth\u00adentication meth\u00adod such\u00ad as STAR\u00adTTLS or SSL.\u00ad\n<\/td><\/tr><tr><td>\n535\n<\/td><td>\nAuth\u00adentication is requ\u00adired but miss\u00ading or inva\u00adlid.\n<\/td><td>\nRevi\u00adew your\u00ad SMTP\u00ad user\u00adname and pass\u00adword and ensu\u00adre prop\u00ader conf\u00adiguration.\n<\/td><\/tr><tr><td>\n538\n<\/td><td>\nEncr\u00adyption is requ\u00adired for the auth\u00adentication proc\u00adess, but was not prov\u00adided.\n<\/td><td>\nEnab\u00adle encr\u00adyption (TLS\u00ad\/SSL) and try send\u00ading agai\u00adn.\n<\/td><\/tr><tr><td>\n540\n<\/td><td>\nThe reci\u00adpient&#8217;s doma\u00adin does\u00ad not have\u00ad DNS reco\u00adrds for emai\u00adl hand\u00adling.\n<\/td><td>\nChec\u00adk the doma\u00adin\u2019s DNS reco\u00adrds or cont\u00adact the doma\u00adin admi\u00adnistrator.\n<\/td><\/tr><tr><td>\n541\n<\/td><td>\nThe reci\u00adpient\u2019s serv\u00ader did not resp\u00adond to the deli\u00advery atte\u00admpt.\n<\/td><td>\nRetr\u00ady late\u00adr or inve\u00adstigate poss\u00adible netw\u00adork issu\u00ades.\n<\/td><\/tr><tr><td>\n542\n<\/td><td>\nThe conn\u00adection was reje\u00adcted due to poor\u00ad conn\u00adection qual\u00adity.\n<\/td><td>\nRetr\u00ady send\u00ading or chec\u00adk your\u00ad netw\u00adork conn\u00adection.\n<\/td><\/tr><tr><td>\n543\n<\/td><td>\nThe rout\u00ading serv\u00ader fail\u00aded to find\u00ad a vali\u00add deli\u00advery path\u00ad.\n<\/td><td>\nRevi\u00adew doma\u00adin DNS and MX reco\u00adrds or cont\u00adact the reci\u00adpient doma\u00adin admi\u00adnistrator.\n<\/td><\/tr><tr><td>\n546\n<\/td><td>\nThe emai\u00adl loop\u00aded betw\u00adeen serv\u00aders and was reje\u00adcted.\n<\/td><td>\nRevi\u00adew mail\u00ad rout\u00ading sett\u00adings to prev\u00adent loop\u00ading scen\u00adarios.\n<\/td><\/tr><tr><td>\n547\n<\/td><td>\nDeli\u00advery time\u00add out afte\u00adr mult\u00adiple fail\u00aded atte\u00admpts.\n<\/td><td>\nRetr\u00ady late\u00adr or inve\u00adstigate serv\u00ader avai\u00adlability.\n<\/td><\/tr><tr><td>\n550\n<\/td><td>\nThe requ\u00adested acti\u00adon was not take\u00adn beca\u00aduse the mail\u00adbox is unav\u00adailable.\n<\/td><td>\nVeri\u00adfy the reci\u00adpient addr\u00adess or cont\u00adact the reci\u00adpient dire\u00adctly.\n<\/td><\/tr><tr><td>\n551\n<\/td><td>\nThe user\u00ad is not loca\u00adl to the reci\u00adpient serv\u00ader and forw\u00adarding is not set up.\n<\/td><td>\nRequ\u00adest an upda\u00adted emai\u00adl addr\u00adess or conf\u00adirm forw\u00adarding is conf\u00adigured.\n<\/td><\/tr><tr><td>\n552\n<\/td><td>\nThe reci\u00adpient\u2019s mail\u00adbox has exce\u00adeded its allo\u00adcated stor\u00adage spac\u00ade.\n<\/td><td>\nAsk the reci\u00adpient to clea\u00adr mail\u00adbox spac\u00ade or retr\u00ady late\u00adr.\n<\/td><\/tr><tr><td>\n553\n<\/td><td>\nThe mail\u00adbox name\u00ad is inva\u00adlid or not allo\u00adwed by the serv\u00ader.\n<\/td><td>\nCorr\u00adect the reci\u00adpient\u2019s emai\u00adl addr\u00adess or chec\u00adk doma\u00adin rest\u00adrictions.\n<\/td><\/tr><tr><td>\n554\n<\/td><td>\nThe tran\u00adsaction fail\u00aded due to a poli\u00adcy or spam\u00ad-related reje\u00adction.\n<\/td><td>\nRevi\u00adew mess\u00adage cont\u00adent, IP repu\u00adtation, and ensu\u00adre comp\u00adliance with\u00ad send\u00ading best\u00ad prac\u00adtices.\n<\/td><\/tr><tr><td>\n555\n<\/td><td>\nThe SMTP\u00ad prot\u00adocol vers\u00adion used\u00ad is not supp\u00adorted by the reci\u00adpient serv\u00ader.\n<\/td><td>\nUpda\u00adte your\u00ad emai\u00adl serv\u00ader to use a comp\u00adatible SMTP\u00ad vers\u00adion.\n<\/td><\/tr><tr><td>\n556\n<\/td><td>\nThe emai\u00adl sent\u00ad is too larg\u00ade for the reci\u00adpient serv\u00ader to hand\u00adle.\n<\/td><td>\nRedu\u00adce the mess\u00adage size\u00ad or use file\u00ad-sharing link\u00ads inst\u00adead of larg\u00ade atta\u00adchments.\n<\/td><\/tr><\/tbody><\/table><\/figure>\n\n<h2 class=\"wp-block-heading\">Wrapping up<\/h2>\n\n<p class=\"wp-block-paragraph\">SMTP error codes may seem complex at first, but they play a big role in helping you understand and troubleshoot email delivery issues. By learning what these codes mean and how to act on them, you can reduce failed sends, improve performance, and keep your email program running smoothly. <\/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_dac4c5571a0261a811ab4a8cb8e24e13\">\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_dac4c5571a0261a811ab4a8cb8e24e13\">\r\n                It&#8217;s easy to get started. And it&#8217;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>Wenn Sie E-Mails in gro\u00dfen Mengen versenden, treten unweigerlich SMTP-Fehler auf. Das Entschl\u00fcsseln dieser Fehler muss jedoch nicht kompliziert sein. Dieser Leitfaden erkl\u00e4rt, was SMTP-Fehlercodes bedeuten, wie Sie h\u00e4ufige Probleme beheben und wie Mailgun Ihnen dabei hilft, den \u00dcberblick zu behalten.<\/p>\n","protected":false},"author":13,"featured_media":4074,"menu_order":0,"template":"","meta":{"_acf_changed":false,"footnotes":""},"blog_category":[20],"class_list":["post-20251","blog","type-blog","status-publish","has-post-thumbnail","hentry","blog_category-email"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>SMTP-Fehlercodes: Vollst\u00e4ndige Liste und Fehlerbehebung - Transactional Email API Service For Developers | Mailgun<\/title>\n<meta name=\"description\" content=\"Lernen Sie SMTP-Fehlercodes verstehen, was sie bedeuten und wie Sie sie beheben, damit Ihre E-Mails reibungslos ankommen. 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