The Problem
You may have set up your spam filter to automatically whitelist e-mails from a specific domain (e.g., mydomain.com). However, you might notice that some e-mails from that domain are still being flagged as spam, for instance, by having their subject line changed to *** SPAM ***.
Understanding the Cause: 'From' vs. 'Return-Path'
This issue occurs when the "From" address displayed in the e-mail does not match the actual sender. Spam filters check an e-mail's headers for its true origin, which is found in the Return-Path field. If the whitelisted address is in the "From" field but a different, un-whitelisted address is in the "Return-Path", the filter will correctly identify it as a potential mismatch and may flag the message.
This is common when e-mails are sent from automated systems or web servers on behalf of a user.
How to Find the Actual Sender
To solve this, you need to find the actual sending address in the e-mail's headers. Most e-mail clients have an option to view the raw headers or the original message source. Look for an option like "View Headers," "Show Original," or "View Message Source."
In the headers, you will find something similar to this example:
Return-path: <[email protected]>
...
Reply-to: [email protected]
From: [email protected]
To: [email protected]
Subject: A test emailThe Solution: Whitelist the Correct Address
In the example above, while the e-mail appears to be from [email protected], the spam filter sees the true sender is [email protected] as specified in the Return-Path.
To prevent these e-mails from being marked as spam, you must add the actual sender address (the one from the "Return-Path") to your spam filter's whitelist.
