Why am I receiving an error about refusing NULL return paths?

Messages from our MDaemon server are sometimes rejected by other servers with a response like this:

Refusing MAIL FROM:<> does not help fight spam, disregards RFC requirements, and stops you from receiving standard bounce messages.

This would happen if you have enabled a setting that used to be visible in MDaemon's GUI, but was later removed due to problems it can create (like the one above). To fix this, open MDaemon\app\MDaemon.ini with Notepad.

Look for RefuseNullReturnPath=Yes

Change the value to RefuseNullReturnPath=No

Save the file and restart MDaemon.

Additional Comments

It is always recommended to create a backup copy of the MDaemon.ini file before making any changes to it.