Why do I receive blank messages?This is caused by some other mail server connecting to your server and sending a . in the data command. You can reproduce by telnetting to your server on port 25 then issue the following commands:
rcpt to: (use a valid alias on your domain)
The message will be accepted for delivery.
This method is probably being used to gather valid email addresses.
The best way to get rid of them is to create a content filter, under the Security button, that checks for:
Where From: message header matches some words (Function: Is String)
and Where To: message header matches some words (Function: Is String)
and Where Subject: message header matches some words (Function: Is String)
If all of these conditions exist, the message will be rejected.
Note: The Function settings in some words will need to be set to Is String, everything else is blank and not checked.
Move the rule to the top of the list or make sure its not below a filter thats set to stop processing.