I know that many lists group addresses by MX to make delivery more
efficient. I've always done this by the name, not the IP address, and
I'm wondering if this is still the norm.
I'm in the process of developing a little spam filtering program, and
it's not only able to filter mail for my domain, but for anyone. The
problem is that it works in real time, sitting between the the client
and the "real" SMTP server. As such, it doesn't do any type of
store-and-forward routine, and thus can only accept and deliver mail
that is truly destined for the server to which it's connecting. It
determines which server to connect to by looking at the domain of the
address in the RCPT command and cross-referencing to a database we
maintain.
For example, this is acceptable, because we host both domains,
RCPT TO:<[EMAIL PROTECTED]>
RCPT TO:<[EMAIL PROTECTED]>
But this would not be acceptable:
RCPT TO:<[EMAIL PROTECTED]>
RCPT TO:<[EMAIL PROTECTED]>
If it were to accept mail - in a single session - that is destined for
more than one SMTP server, it would be unable to deliver to all the
recipients. In the latter example above, the second address would
generate a temporary failure response, which I'd like to avoid. I also
cannot dump everything to a smart host, because the smart host would
always deliver it right back to the filter.
So what I'd like to do is setup CNAME records for each domain that will
use the filter, and have them all point to the same place.
For example:
greatcircle.com MX 0 greatcircle.inbound.vansys.com
greatcircle.com MX 100 honor.greatcircle.com
vansys.com MX 0 vansys.inbound.vansys.com
vansys.com MX 10 titan.vansys.com
vansys.inbound.vansys.com CNAME
aurorafilter.vansys.com
greatcircle.inbound.vansys.com CNAME aurorafilter.vansys.com
aurorafilter.vansys.com A 207.6.137.???
My hope is that the MTA's out there will deliver the second example
message in two separate session.
Any thoughts?
Rick Vandenberg
