>I know this, it's very clear. I used Outlook Express 5.5 to send a mesg to
>an unknown user, and then I got the following mesg.
>
>......: '550 unknown user <[EMAIL PROTECTED]>', ............
ok, 5xx is fatal. the sender should not retry.
>But when a mailing list send a mesg to an unknown user, the sender won't get
>this message, that will be a problem. Any idea?
In my experience, many mailing list manager programs, and/or their
operators/admins, are so stone-stupid that they will bang on forever
sending to an address after the recipient's mail server returns "550
unknown user". The MLM's "bounce management" routines should
automatically stop harassing the mail server that returns a 5xx.
The other case is spammers using cdroms and other lists where 1000's
of the mail accounts are closed / dead, but mail server is still
there and must bounce 1000's of msgs per day (I have recent
experience with one ISP using IMgate who gets 20K msgs/day to unknown
users, with sometimes 100's of msgs to the same dead account).
There is really no interest or payback in being polite and
intelligent in these situations. The sender is probably not paying
attention anyway.
Imail sends 550, end of story.
Len
http://BIND8NT.MEIway.com : ISC BIND 8.2.2 p5 & 8.2.3 T6B for NT4 & W2K
http://IMGate.MEIway.com : Build free, hi-perf, anti-spam mail gateways
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