Emails being marked as spam is a common issue faced by many users. This can occur due to various reasons, from the originating domain name being blacklisted to the recipient mail host requiring additional validation. This guide will help you understand why this happens and how to resolve it.

Common Reasons for Emails Being Marked as Spam

Your Domain is Blacklisted

If your domain name has been blacklisted, it can cause issues with email delivery. You can check if your domain has been blacklisted using tools like MX Toolbox. If your domain is blacklisted, you would need to find out the reason behind this and resolve it as a matter of urgency to avoid your messages being marked as spam.

Your Server's IP Address is Blacklisted

If your server's IP address has been blacklisted, the receiving mailbox may consider your message as spam. This is a common problem in shared hosting environments, as your IP address is shared with multiple users. At Brixly, we use a service called MailChannels, a premium SMTP relay, to route all emails and avoid the issue of messages not being delivered or being marked as spam due to blacklisted IP addresses.

The Recipient Mail Host Requires Additional Validation

The recipient mail host might require additional validation, such as the existence of SPF or DKIM for your domain. You can use online services like Mail Tester or Experte's Spam Checker to diagnose if this is the cause of your emails being marked as spam.

Custom Anti-Spam Filters Applied by the Recipient Email Host

Custom anti-spam filters applied by the recipient email host might also end up rejecting an email based on its contents (subject, body, attachments, etc.). This issue would need to be addressed by the recipient, to ensure the contents of your emails are no longer filtered.

Diagnosing Why a Message Has Been Marked as Spam

If you are still unsure as to why your emails are being marked as spam, ask the recipient to provide you with the email headers for the email received. When raising a support ticket regarding your outbound messages being received as spam by a third party, please ensure you also provide the details of the email, such as the sender, recipient, subject, and time/date. You must also include the email headers for us to be able to attempt to diagnose the cause for the message being received as spam.

Please note, however, that not all providers will store sufficient detail within the email headers themselves and may need to be raised with the third-party/recipient provider for further information.


Mail Tester is an online service that provides a comprehensive analysis of your emails. It checks for potential issues that could lead to your emails being marked as spam, such as problems with your SPF records, DKIM signature, and content.

To use Mail Tester:

  1. Visit the Mail Tester website.
  2. You will be provided with a temporary email address. Send a test email to this address.
  3. Go back to the Mail Tester website and click on "Then check your score."
  4. You will be provided with a score out of 10 and a detailed report of your email.

The report will inform you whether the issue is relating to SPF under the 'Authentication' section. Note: when using, please ensure you enter some valid content in your message being sent, to ensure the score isn’t negatively impacted due to missing or spam-related content.

By using Mail Tester, you can gain insights into why your emails might be marked as spam and take steps to improve your email deliverability.

By understanding the cause of your emails being marked as spam and following these solutions, you can improve your email deliverability and reduce the likelihood of your messages being incorrectly marked as spam.