Domain of sender address ... does not exist

[Greg Woods]

On Fri, 2009-12-11 at 18:02 -0500, Tony Nelson wrote:
> there is no requirement that a 
> domain have an A record to exchange mail

True, but there are plenty of mail servers (including sourceforge.net)
that verify DNS information by back connecting. The domain therefore has
to either have an A record, or an MX record pointing to a server that
does have an A record, and the server the MX points to (or A if no MX)
must be reachable on the SMTP port. We have found this out because we
modify all MX records to point to our gateway, and we've had people send
mail out from machines we weren't told were mail originators (and
therefore they have no MX), and since the SMTP servers on these machines
are not reachable from outside, mail servers like sourceforge.net refuse
to accept mail from these hosts. So it is possible to have your outgoing
mail rejected due to DNS inconsistencies.

--Greg