Gmail troubleshooting support information

This article provides information about troubleshooting email delivery problems at Gmail, including spam folder placement and error codes.

 Gmail troubleshooting tools

Spam folder placement

The best way to ensure mail is delivered to Gmail subscribers is to comply with its bulk sender guidelines.

Basic steps to troubleshoot bulking at Gmail

Here are some troubleshooting steps you should take if you are experiencing spam folder placement at Gmail.

  • Are you are signed up with the Gmail complaint feedback loop (FBL) and actively reviewing the data?
    • You can sign up at the Gmail Postmaster website. High volume senders can use the Gmail FBL to identify problematic campaigns causing high complaints.
  • Did you recently start sending from a new IP address or domain? Neglecting to warm up your new IP address or domain causes email to be sent to the spam folder. 
    • Warming up your IP or domain too fast can also make you look like a spammer and lead to spam folder placement.
    • Gmail's spam filter needs time to learn how subscribers interact with your email to help it determine where to place your email.
    • Be sure you are warming up your IP or domain with engaged subscribers who will open and interact with your email.
  • Are you sending to subscribers that are engaged with your email?
    • Sending to a lot of subscribers that have not engaged with your email (i.e. opened and read, saved from the spam folder, replied to) recently can cause email to be sent to the spam folder. Some senders have success at Gmail by being very aggressive with sending to engaged subscribers. Try sending only to subscribers that have engaged within the last 6 months. If you don't see improvement in inbox placement, go to 5 months, 4 months (etc.) until you see a change in inbox placement. If you have bad deliverability problems at Gmail, you may have to temporarily only send to users that have engaged within the last 15 to 30 days to help improve your sending reputation. As inbox placement improves you can start adding in less engaged users slowly so as not to sabotage any progress. 
      • If you notice an engagement threshold at Gmail (e.g. engaged within the last 90 or 180 days) where performance starts to suffer, rethink your content strategy to keep more of your subscribers engaged over time. Engagement is important to Gmail as it is a reliable indicator that you are less likely a spammer and more trustworthy.
  • Check your triggered email rules.
    • Triggered emails and their influence on your sending reputation and inbox placement are sometimes forgotten since they occur automatically. Check the rules in place for potential frequency issues (too much) as well as sending to unengaged subscribers (like for a birthday, anniversary, renewal reminder, etc.).
  • Are you sending too frequently?
    • If you are sending every day or multiple times a week you may want to try reducing the frequency to see if there is any benefit to your complaint rate.
  • Do you have an unsubscribe link at the top of your email?
    • Some senders see a benefit by adding another unsubscribe link to the top of the email, this makes it easier for a subscriber to unsubscribe instead of mark the email as spam.
  • Do you make frequent adjustments to your email program?
    • Frequent changes to your sending behavior and identity makes you look like a spammer. Such as:
      • Frequency (common around the holidays)
      • Volume
      • Sending domain
      • DKIM domain
      • Sending IPs        
  • Did you acquire email addresses from a high risk source? 
    • Look at any subscriber lists that have been recently added to your list file. Addresses acquired through a list purchase, list harvesting or co-registration (with a partner that does not follow best practices) causes deliverability problems at Gmail.
  • Are your domains blacklisted?
    • Gmail cares about protecting their users from phishing email and dangerous websites. Although Gmail doesn’t publicly disclose how they identify dangerous websites, you can check:

Check all domains in your header as well as within the content.

  • Are you authenticating all of your email and is it passing verification? 
    • Ensure you are authenticating with Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication Reporting & Conformance (DMARC). Ensure that there are no configuration errors in all of the authentication methods or it could lead to messages sent to the spam folder. 
      • View the Gmail email header for one of the Gmail CoreSeeds in Return Path Platform. A successful verification looks like this:

spf=pass ( domain of designates {IP address} as permitted sender);
dmarc=pass (p=NONE dis=NONE)

If any authentication is failing verification, investigate and fix the cause.

How long will it take to get back to the inbox?

It depends on the seriousness of the issue.

Inbox recovery may take anywhere from a month to three months once you have found the cause. Gmail will not reset a sender's reputation. It fully trusts that its system will adapt to subscriber response and determine where mail should be delivered.

Public escalation

To help ensure that mail is delivered to Gmail users, you need to comply with Gmail's bulk sender guidelines. If mail is sent according to the guidelines and Gmail continues to mark messages as spam, contact the Gmail team by filling out the Bulk Sender Contact Form.

Before submitting the form, ensure that you are following all of Gmail's bulk sender guidelines and that there are no obvious issues with complaints or engagement.

Although Gmail will not inform you about their investigation or findings, they may make adjustments to improve their spam filter.

SMTP error codes

  • Track and monitor bounce message error codes from Gmail in order to help identify and fix issues. They can be an important indicator to Gmail about the health of your email program.
  • Gmail SMTP error codes.

Common error codes for mail blocked as spam:

  • 550 5.7.1 Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been blocked.
  • 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been *{*}temporarily* blocked.

When receiving these errors:

  • The codes mean that something needs attention according to Gmail, so try to investigate and fix the cause immediately.
  • If your email is blocked, stop sending for 24 hours so you can investigate and fix the cause.
  • Review your email address acquisition process and ensure email is only sent to people who opt-in to receive your email.
  • Review the management policy for sending to inactive subscribers and ensure mail is only sent to people who still want to receive it. You may have to temporarily only send to users that have engaged within the last 15 to 30 days to help improve your sending reputation.
  • Ensure you follow Gmail's bulk sender guidelines.

Connection and throughput errors:

  • Message Expired DOMAIN UNRESPONSIVE MX ERROR. Connection to MX server - lost during <SMTP> <banner> transaction.

Lower connection volumes and decrease throughput speed. Suggested connection and throughput settings are:

  • 150 connections
  • 50 messages per connection

However, depending on your sending reputation, you may have to lower your settings until you stop seeing the error.

Delivery delays

If your email campaign is taking longer than expected to reach its destination, Gmail's Header Analyzer can help you identify a possible cause. It may indicate a traffic jam in your sending system or if Gmail's servers may be experiencing some processing issues.

DMARC failures

  • 550 5.7.1 Unauthenticated email is not accepted from this domain.

Gmail will block any email purporting to come from a domain that has a p=reject DMARC policy if it does not actually come from that domain. This can happen if you use a From domain such as or To prevent this from happening you should only use domains that you have full control of or have authority to use.

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