David Walker wrote:
I don't understand why mail servers treat bounces as regular messages.
I believe that your mail server should encapsulate a bounce message in a
generic "here is a mail error" report.
They do exactly that. Problem being that the "generic here is a mail
error" technique also happens to have a desirable feature for spammers -
no bounce back, aka the <> envelope sender.
Bouncing email simply because it has an envelope sender of <> is truly a
bad idea over and above the fact that the RFC states you shouldn't. Eg:
double bounces to postmaster. Your users not seeing NDRs when they
should. Missing vacation messages etc.
However, you can finesse this somewhat. We inline reject <> envelope
from in the following two circumstances:
1) The From: has no "@", or doesn't contain "mailer-daemon"
or "postmaster", or,
2) There's multiple RCPT TOs (recipients).
No FPs ever on (1). Only two FPs on (2) - broken mailing lists, which
we assisted the listowner in fixing. Quite happy with both rules.
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