When sending emails, you may occasionally encounter an error message stating, "550 This message was classified as SPAM and may not be delivered." This error occurs when the email you're trying to send is flagged by our spam detection procedures. This guide will help you understand why this happens and how to resolve it.

Why Does This Error Occur?

To combat the global issue of spam, we have implemented spam detection procedures on all emails before they leave our servers. Each email is evaluated and rated according to spam rules to determine how likely they are to be actual spam. Emails that fail the test are returned to the original sender with the "550 This message was classified as SPAM" error message.

We screen outbound emails to help preserve the reputation of our server’s IP addresses. Once a mail IP gets enough spam complaints against it, it can be reported to a company that maintains a blacklist. Any email server that subscribes to that particular service will then block any incoming email from that IP address.

How to Resolve the Error

If you encounter this error, there are a couple of solutions you can try:

Solution #1 – Enable SMTP Authentication in Outlook

If you are using the Microsoft Outlook email client, not having SMTP Authentication will cause several points to be added to the spam score. This can cause emails that otherwise would be allowed through to be classified as spam. You can enable SMTP Authentication by following the instructions in our Invalid HELO name article.

Solution #2 – Evaluate Email Content

As our outgoing servers are using a spam evaluation software set at the most lenient levels, it is difficult for your emails to be tagged as spam and prevented from going out unless they have a lot of features of a spam message. If you are getting caught by the filter, evaluate both the title and body content of the message to ensure there are few, if any, references to popular spamming terms.

By understanding the cause of the "550 This message was classified as SPAM" error and following these solutions, you can improve your email deliverability and reduce the likelihood of your messages being incorrectly marked as spam.