Sometime Today, Sameer D. Sahasrabuddhe assembled some asciibets to say:
S<the email address you send with>
What does that do, set the ENVELOPE SENDER field (I am not sure if I got the name correct)? I believe that is very easy to modify in
It changes what goes in the MAIL FROM: line without changing the header of the message. Changing all of them is easy in sendmail. I believe that there are ways to change them separately too, as there are separate rulesets for changing envelopes and headers (S10 and S11), while a single ruleset to rewrite sender's address (S1).
Philip