550 The content of this message looked like spam

The error message '550 the content of this message looked like spam' indicates that the sent email could not be delivered because the receiving spam filter classified it as SPAM. This classification is typically well-founded.

Every email is scored by the spam filter using a specific algorithm. The score is based on various criteria, such as:

• The reputation of the sending mail server, for example, whether it is listed on a blacklist.
• Whether the content contains harmful elements, such as malware in the attachments.
• The content itself, including specific language resembling spam or links to blacklisted (phishing) sites.

This algorithm is highly accurate and leverages a vast database of processed emails, numbering in the millions. If the score of a message exceeds the preset threshold, it is classified as SPAM. The error message ‘550’ is then sent back to the sender to inform them of the failed delivery.

Below, we outline the two most common causes of the '550 the content of this message looked like spam' error message and how to address them.

Step 1: Verify the SMTP Server Settings

Most incoming spam filters use the mentioned algorithm to check whether authentication is required for the sending server, which is often the case with legitimate SMTP servers.

In your email program, go to the SMTP settings (outgoing email) in the advanced options. Look for an option with wording like “This server requires authentication” or something similar. Enable this option, restart your email program, and try sending the email again.

If this does not resolve the issue, proceed to Step 2.

Step 2: Check the Content of the Email

Ensure the email does not contain content or attachments that might trigger spam filters. Here are some examples:

• Untrustworthy content: Avoid using spam-like words or formatting in your email.
• Excessive links: Too many hyperlinks in your email can be flagged as spam. Limit the number of links you include.
• Large attachments: Emails with large attachments may be deemed suspicious. Consider using links to shared files instead of attaching files directly.

Note: It’s also possible that your computer has been hacked. Check all devices where the email address is configured for malware or harmful software. There are several (free) programs available to help with this, such as Microsoft Security Essentials, AVG, Malwarebytes, or similar tools.