Egress spam filtering E-mail senders can do the same type of
anti-spam checks e-mail coming from their users and customers as can be done for e-mail coming from the rest of the Internet.
Limit e-mail backscatter
If any sort of bounce message or anti-virus warning gets sent to a forged email address, the result will be e-mail backscatter.
-
Problems with sending challenges to forged e-mail addresses can be greatly reduced by not creating a new message that contains the challenge. Instead, the challenge can be placed in the Bounce message when the receiving mail system gives a rejection-code during the SMTP session. When the receiving mail system rejects an e-mail this way, it is the sending system that actually creates the bounce message. As a result, the bounce message will almost always be sent to the real sender, and it will be in a format and language that the sender will usually recognize.
