[cobalt-users] SPAM and AV filtering on a per-domain basis via two servers?

["David Thacker" <Cobalt@xxxxxxxxxxxxxx>]

Hi all,

I've got a RaQ3 hosting various cutsomer sites for DNS, web and email, and a
RaQ4 server for data backup, secondary DNS and backup MX service.  [Yes, I
know the RaQ4 should be the primary server for lots of reasons, but ignore
that.]

I've been thinking about adding the Solarspeed AV & AntiSpam packages, but
they work on a server-wide basis, not per-domain.  I know I could install
SpamAssassin and MailScanner plus an AV package manually, but I quite like
the per-user GUI additions that the Solarspeed package offers.  The trouble
is, I want to be able to charge hosting customers a premium for mail
scanning capability, but I know some will want to pay for it and some won't,
and I don't want those that don't want to pay to get the service for free.

So, we're finally getting to my question... Can I conceivably change the MX
records to enable this scenario:

1. RaQ3 keeps all user accounts and is POP3 server for all domains
2. RaQ4 becomes SPAM/AV filtering mail server (after installing Solarspeed
pkg)
3. set higher priority MX to RaQ4 for domains that pay for scanning service
4. leave higher priority MX at RaQ3 for domains not to be scanned
5. users make no change to email client settings for POP server

6. after mail is scanned on RaQ4, gets forwarded to RaQ3 for depositing into
existing user mailboxes

7. if mail happens to go to lower priority MX server (very infrequent per my
server logs) then it either gets scanned for free or doesn't get scanned but
either way still ends up in user mailbox on RaQ3


The only point that I have a question about is #6: how do I make the RaQ4
server listed as the high priority MX receiver for a domain forward the mail
to the lower priority server once it has scanned the mail, so that it ends
up in the user mailboxes?

Any ideas?

David Thacker