Apparently Bruce found a minor problem in 2821, it's not 110%
clear what to put in the Return-Path for a null MAIL FROM:<>
hmm, you put exactly what the Reverse Path (MAIL FROM) provided.
Return-Path was only meant for final destination mail as a way to provide a
post smtp system (i.e., gateway) a method to initiate a bounce process using
the proper reverse address that was not typically available using the older
There is no bounce process for a NULL reverse address (return path).
Also, the Return-Path is typically removed once the gate sees its a normal
message (no bounce requiired) before final storage for the end-user. It is
not required any more at that point.
Before, the gate had to play games like maybe checking for an
administrative address (Mailer-Daemon, PostMaster) in "822.From:"
A null return path, "Return-Path: <>", a clear indication of a non-bouncing
Hector Santos, Santronics Software, Inc.