Scott Kitterman writes:
On 11/29/2005 07:16, paddy wrote:
Only if the remote MTA cannot be reached should the
message be accepted and stored for later delivery.
yes, a key reason why its hard to see why bounces should go away entirely.
Yes, but very much a corner case at most. Border MTAs should have all the
information necessary to determine if a message is acceptable to deliver
(e.g. list of valid users). The only time this might be appropriate is in
the case of multi-hop e-mail accross administrative boundries.
Even a list of valid users won't eliminate bounces. That a user is
valid doesn't mean his/her mailbox isn't over quota or isn't forwarded
to a mailbox that's over quota or to one that's temporarily disabled
but returning 5xx error codes.
The on-the-fly delivery concept is also fatally flawed. The very
reason for having multiple MXs is to receive mail when the primary MX
is too busy to accept new connections.
My small mail service has from three to five border MTAs, depending on
which domain the mail is for, and I try hard to reject mail rather
than bounce mail. Keeping things in sync isn't easy. Either each MTA
needs its own copy of the valid address database or validity checking
has to be available as a network service. Both approaches have
weaknesses keeping up with changes as users come and go and forwarding
addresses change status.
Bounces can be greatly reduced but not eliminated completely.
--
Dick St.Peters, stpeters(_at_)NetHeaven(_dot_)com
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