At 14:13 01-05-2007, Peter J. Holzer wrote:
that verification can be done even if xyz is down if foo has the
necessary information.
That's not always possible. For example, New Orleans is
flooded. You set up a MX for the domain until further notice. foo
cannot get the necessary information for recipient
verification. This was an actual case.
So if the backup mx syncs frequently with the primary mx it should a
good idea which addresses are valid and which aren't. Frequently the
That's a best practice.
Also true, but a backup MX which has a different configuration than the
primary is worse than none in many (most?) situations. The days where
"accept everything for domain X and relay it to a lower numbered MX" was
a useful backup MX configuration are unfortunately over.
Yes. The main problem is that the backup MX may have a less
restrictive filtering policy than the lower numbered MX.
Many of the problems described above can be avoided by not accepting
a mail in the first place. An SMTP server (especially one acting as
MX) SHOULD make every reasonable efford to determine whether the
message will be delivered to the recipients mailbox and reject the
the message during the SMTP transaction if that is not the case.
Yes. But that may be construed as forbidding bounces
altogether. This makes existing mail servers non-compliant overnight.
Regards,
-sm