OK, I got this working! (Persistence pays off...)
On the backup MX, I made sure that $mydestination was correctly set, and
then set $local_transport to "smtp:nexthop:port"
On the primary server, I created a new smtpd transport (listener)
[xxxx:xxxx:xxxx:xxxx::x]:xxxx inet n - n - - smtpd
-o smtpd_client_restrictions=permit_mynetworks,reject
This new transport replaces the client restrictions specified in main.cf
(which invoke the dspam filter), so mail arriving on this listener will
not get filtered.
Simple when looking at it in retrospect. But you have to admit that
postfix configuration can be rather daunting or intimidating if you're
doing it for the first time...
I would have preferred to include the "default" client restrictions in
master.cf as well, but it kep complaining about the following:
[addr] inet n - n - - smtpd
-o smtpd_client_restrictions=check_client_access regexp:/path
I suspected that the space character was the problem, so I tried to
put the value all in quotes, but that didn't help.
+------------------+--------------------------+------------------------+
| Paul Goyette | PGP Key fingerprint: | E-mail addresses: |
| (Retired) | FA29 0E3B 35AF E8AE 6651 | paul at whooppee.com |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd.org |
+------------------+--------------------------+------------------------+
