>Strange, if you look at RFC821 4.3 page 37 "Command-Reply Sequences":
>
> CONNECTION ESTABLISHMENT
> S: 220
> F: 421
>
>That means that Symantec Firewall only can reply 421 to Imail if there is a
>error before HELO.
>
>Correct??
RFC2821 4.3.2 updates RFC821 to allow a 554 response (although I don't
believe 2821 is technically a standard yet).
So the two ways that it can be handled properly are [1] Send a 554 response
(which some mailservers may not handle correctly), [2] Send a 421 (in which
case mailservers should try again later with the same mailserver), or [3]
Don't accept the connection.
In the case of the huge ISP, the best answer would be for them to take out
the primary MX record (since it is designed not to accept mail, it
definitely should not be in the MX record). If they still want it listed
in the MX record, and feel that the extra bandwidth is acceptable, the
should simply drop the connection (which uses the least
bandwidth). Otherwise, they can use the 554 (which uses more bandwidth and
some mailservers may not handle correctly) or keep using 421 (which uses
lots more bandwidth and will cause lots of their mail to bounce).
-Scott
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