Chris Ross wrote:
>   Does anyone have any idea what's gone on here?
> 
>   If I insert the IPv6 address into the relevant line of sendmail.cf
> (instead of leaving
> Addr=mail.distal.com), sendmail comes up and works just fine.  So, it's
> clearly
> some sort of resolution problem...

Hi Chris,

I think you're right in that it looks like your box can get a v4 address
for mail.distal.com but can't get a v6 address for it.  I tested this
myself with a default 8.13.5 config and came across the same issue.  I
usually use IPv4/IPv6 addresses as arguments to Addr, not hostnames, so
I can only guess as to why your seeing the different behaviour between
8.13.3 on 2.1 and 8.13.5 on 3.0.  Some ideas:

The hosts files could have been different between the two boxes i.e. one
included a v6 entry for mail.distal.com and the other didn't.

One of the DaemonPortOptions could have included a Modifier=O which will
silently fail when trying to bind to the v6 address but still run.

If you specify IP addresses for the Addr options then the problem should
go away.

HTH,

adrian.