The only snag with sending reject replies is that it's then open to
abuse. If I took a dislike to someone (not a subscriber), I could send
hundreds of emails to the list, spoofing his email address as the
sender. He'd then get his inbox swamped.
âI disagree, and cite precedent in use by other mailing lists. If the targeted user is on the mailing list, there is no rejection notice. If not, then the attack is no different from any of the related variety of backscatter mailer exploits.
I personally subscribe to the view of RFC 5321: As discussed in Section 7.8 and Section 7.9 below, dropping mail
without notification of the sender is permitted in practice. However, it
is extremely dangerous and violates a long tradition and community
expectations that mail is either delivered or returned. . . . silent dropping of
messages should be considered only in those cases where there is very
high confidence that the messages are seriously fraudulent or otherwise
inappropriate.