[exim] Exim4 (x2) and mail relay unusual behaviour

Hello all,

Please feel free to redirect if this is the wrong list or area.

Here's my problem. Primary domain name: mydomain.com.au has 2 MX records (primary and secondary/backup mail server).

mydomain.com.au IN A 192.168.1.1

mail.mydomain.com.au IN MX 10 192.168.1.100
mail2.mydomain.com.au IN MX 20 192.168.1.110

Both mail servers have Exim4 installed (different version on each - long story) and running on Debian Lenny. Something is happening and I do not understand why, perhaps someone can shed some light?

Both mail and mail2 have the exim configuration files (mail uses update-exim4.conf.conf and the variables fill in the DEBCONF template. mail2 has a 'configure' file in /usr/local/etc/exim)

mail2 has a domainlist relay_to_domains that includes a domain name we host myotherdomain.com.au
mail does not have this entry in dc_relay_domains field.

Yet, and here's the twist, until recently we were successfully receiving mail for fred@??? - despite there being no domain relay allow type rule in exim4 on the primary mail server. Just on the secondary mail server.

Does that all make sense? Hope so. Would really like to know what's happening here.

Thank you kindly!

Edward
edward AT onereason.com.au