[Mimedefang] Adding support for learning our addresses

[Damrose, Mark]

> -----Original Message-----
> From: Matthew.van.Eerde at hbinc.com

> > the internal and external DNS for my namespace are maintained on 
> > separate servers.
> 
> Hence services like www.whatismyip.com

http runs through a proxy server, so I would get a different public
IP than SMTP sessions use to reach the mail server.  Not that I would
have any significant filter logic rely on a service whose format, 
existence, and reachability could change at any time.

There's so much to set up on a new server, that I have a hard time
seeing the benefit of jumping through a lot of hoops to have the
same filter run unmodified on several at once.  I suppose that
if you wanted to push out changes to a cluster of mimedefang boxes
and have some filter logic that knows your own IP, then put it
in /etc/mail/mimedefang-filter-local, and source it as a library.

> What I think would be really nice is a new kind of DNS 
> record... something like WHOAMI... that provides this kind of 
> a service.  So for example
> 
> dig -t WHOAMI your-friendly-neighborhood-dns-server.example.com

That has some interesting possibilities.  NAT aside, it would be
nice to know sometimes - even on a multi-homed server which 
address was used for a particular connection.  I don't necessarily
agree that DNS is the place to fit this, but it's an idea that's
worth developing.