what do the mail logs say about this particular mail?

(Name service error for machine1.mynetwork: Host not found, try again) bjsamuels@beenthere-donethat.org.uk

is machine1 acting as an smtp relay or just an ipv4 gateway?

I used eximconfig, supplied with Debian, to set exim up as a relay. In the exim.conf I have:

# The setting below allows your host to be used as a mail relay by only # the hosts in the specified networks. See the section of the manual # entitled "Control of relaying" for more info.

host_accept_relay = 127.0.0.1 : ::::1 : 192.168.1.0

I also have:

local_domains = localhost:mynetwork

What makes me think that the problem my be on machine1 is that if I try to send an email from machine1 (Exim) to a user on machine2 (Postfix), e.g. amanda@machine2.mynetwork, it fails. It actually sends it out to the Internet which, of course, fails. I don't know why it apparently ignores the local_domains setting.

is exim set up to avoid dns mx lookups for itself and machine2?

I wouldn't know. I would assume that the local_domains bit above should do that although it doesn't seem to work.

Barry Samuels