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Why is Gmail blocking my emails? How to prevent it

As a leading mailbox provider, Gmail often calls the shots and sets the industry standard for protocols that control who gets into the inbox, and which messages get blocked. If this is happening to you, don’t worry. There are steps you can take to get back on Gmail’s good side.



It's frustrating as an email sender when your messages don’t get through. Especially if you don't know why it's happening. In this article, we’ll dig into why Gmail may be blocking your emails, cover some of the new Gmail inbox protocols, and leave you with some suggestions on how to improve your email deliverability. The inbox world is selective. Trust us, you’ll want these tips.

Why is Gmail blocking emails?

So, you’re frustrated with blocked emails on Gmail. After all, you’re not a spammer, so why is this happening to you? Not only are there many possible culprits, but some of the reasons have bigger consequences than they used to due to Gmail inbox updates and new sender requirements being implemented in early 2024. If you’re emails are being blocked and your spam complaint rate gets too high as a result, you could find that all of your messages start making their way directly to the spam folder.

With the new sender requirements implemented by Gmail and Yahoo, stricter authentication protocols like DMARC are now being enforced to verify the legitimacy of bulk senders. Other requirements such as a cap on acceptable spam complaint rates, and enforcement of a one-click unsubscribe link may result in more legitimate senders being viewed as spammers.

Here are the most common reasons why Gmail might be blocking your emails:

  • Your email contains too many images

  • Your email contains an unapproved attachment type

  • Your email doesn’t have a subject line

  • Your email contains unapproved HTML

  • Your email contains a virus

  • Your IP address is on a blocklist

  • You have a bad IP reputation or sender reputation

  • You have a high bounce rate

Learn more: Inboxes are updating their protocols and cracking down on spam by making SPF, DKIM, and DMARC authentications mandatory and by setting stricter standards for spam rates and unsubscribe processes. We’ve got everything you need to know to prepare in our Gmail and Yahoo inbox updates post.

Let’s look at each of these in detail.

Your email contains too many images.

Gmail imposes a limit of 25Mb per image and 100 images per email. If you include multiple images, try to reduce the number to keep your email under the limit. Besides, emails with a high number of images might get flagged as spam. If you’re not a spammer, avoid sending out spammy-looking content! Otherwise, you might land in Gmail’s spam folder.

Your email contains an unapproved attachment type.

Gmail doesn't allow certain types of attachments, like .exe files and .zip files. If you're trying to include an attachment that's not allowed, you'll need to find another way to send it.

Your email doesn’t have a subject line.

If your email is missing a subject, Gmail will automatically block it. This is because emails without subject lines are often spam emails. Fix your subject lines to dodge the spam filter. Check out our tools to make sure your subject lines pass muster!

Your email contains unapproved HTML.

Gmail doesn't allow certain types of HTML in emails, including:

  • Javascript

  • ActiveX controls

  • Flash

If your email contains HTML that's not allowed, try removing it and resending the email.

Your email contains a virus.

Gmail has a built-in virus scanner that will block emails that contain viruses. If your email is being blocked because it contains a virus, you'll need to remove it before sending the email.

Your server’s IP address is on a blocklist.

If you’ve ended up on Gmail’s blocklist, your message might be blocked by Gmail. Learn more about blocklists, delist your IP address if you’ve landed on a blocklist.

You have a bad IP reputation or sender reputation.

If you’ve been acting like a spammer by sending high volumes of content to inactive or invalid email addresses, your IP and sender reputations suffer. Moreover, if you’ve received a high volume of spam complaints from your subscribers, Gmail might decide not to deliver your emails.

Gmail’s advanced filtering systems analyze email content and sender behavior overall, flagging suspicious emails and blocking those that don’t comply with all of the requirements collectively. Consistency is the key. If you consistently send in compliance with Gmail standards, the occasional spike in complaint rate on a campaign will hurt you much less than if your practices constantly raise flags.

You have a high bounce rate.

If too many of your emails bounce back, Gmail may refuse to deliver your emails. Keep your bounce rates low to keep your deliverability high.

How to prevent Gmail from blocking emails?

If Gmail is blocking incoming emails from you, it’s not the end of the world. Here are some Gmail best practices to prevent blocked messages in Gmail:

Use email authentication: Ensure your DMARC, DKIM, and SPF are properly set up. These are your “ID cards” for sending emails, and make sure to set up your Domain Name Service (DNS) record to display your sender’s name. This way, Gmail knows you are who you say you are and is less likely to flag you as a spammer.

Gmail and Yahoo both require bulk senders to have implemented DMARC with a policy of p=none. Learn more in our post on DMARC.

Provide a single-click process for subscribers to unsubscribe. If your subscribers aren’t given a way to opt out with a single click, Gmail will flag you and your users might just mark your email messages as spam. While this doesn’t mean much for your recipients (they get the same result: not seeing your emails land in their email account), too many spam complaints can land you on a blocklist. And any spam rate higher than 0.3% will land you in the spam folder according to the new Gmail inbox protocols.

One-click unsubscribe must follow RFC 8058. Learn how to implement it in our post on RFC 8058.

Clean your email list: Maintain your email list hygiene by regularly verifying email addresses and removing invalid users. This way, you can reduce your email bounce rate and improve your deliverability.

A regularly validated email list helps ensure your recipients want your messages and leads to lower spam rates. Learn more in our post on list hygiene.

Monitor Google Postmaster: Monitor your messages to Gmail with Google Postmaster Tools to track metrics around open rate, click-through rate, bounce rate, conversions, engagement, and authentication status. Especially with enhanced inbox protocols, monitoring for specific inboxes will be key in maintaining a strong sender reputation.

Monitoring your sending is critical to stay within acceptable limits and maintain a good sender reputation. Learn how you can monitor your Gmail sending from within your Mailgun account without our Google Postmaster integration.

Wrapping up

There are many reasons Gmail can block your emails, and a few tried and true paths to get unblocked. It’s also possible that the reason you’re messages are being blocked are not easily solved by our reasons in this post. Deliverability is nothing if not compelx. Need more help? Take advantage of our deliverability services and the InboxReady Google Postmaster Tools to see how Gmail perceives your reputation and manages your incoming messages.

With Google Postmaster Tools now integrated into the Mailgun Optimize suite, you get access to your most essential testing and monitoring tools, all in one convenient place. What better way to improve your Gmail deliverability than using the tools Gmail provides?

Google Postmaster Tools is integrated with Mailgun Optimize

The Mailgun Optimize suite was built to help senders tackle the most common issues preventing them from landing in the inbox. Now we're taking it one step further by providing visibility into your most essential email analytics with Google Postmaster Tools in Mailgun Optimize.

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