When a web app calls mutt (with no .muttrc) to send email, the result contains headers of the form
(where 'name' and 'host' are the user and server where the app is installed)
But firstname.lastname@example.org is not a working email address (in the sense that trying to send email to such an address from gmail yields "Your message couldn't be delivered ... because the remote server is misconfigured ... The response from the remote server was: ... Relay access denied")
One can correct the 'From' header by using the mutt option
-e 'my_hdr From:email@example.com'
but trying the same thing for Return-Path has no effect.
Why do I think a misconfigured (or at least questionable) Return-Path header could be a problem?
(1) it could reduce the deliverability of the mail if the remote server checks the headers thoroughly
(2) if the mail is undelivered, it would reduce the chances of a failure notification being sent back