Backup Mail Server Questions

Ted Mittelstaedt tedm at
Sun Sep 26 21:24:37 PDT 2004

> -----Original Message-----
> From: owner-freebsd-questions at
> [mailto:owner-freebsd-questions at]On Behalf Of Chuck Swiger
> Sent: Sunday, September 26, 2004 12:29 PM
> To: Eric Crist
> Cc: freebsd-questions at
> Subject: Re: Backup Mail Server Questions
> Eric Crist wrote:
> [ ... ]
> > One of my friends needs backup DNS/Mail in the even their connection
> > goes down.  How do I go about setting it up so that his user
> base (about
> > 80 users) will not see any problems in mail transmission and reception
> > if their primary servers go offline.  I would like mine to
> automatically
> > pickup the slack.
> Setting up redundant DNS is trivial: DNS is designed to do that.
> Setting up a backup MX is easy.  It helps a lot if both mailservers are
> configured the same, and it is important that they have near-identical
> anti-spam and virus-filtering technologies.
> Setting up a truly redundant POP/IMAP reader box is extremely hard.
> To solve this problem for a local network, one normally uses a
> shared NAS box:
> in your case, this effectively requires one to set up a
> network-distributed
> filesystem, or some near-equivalent: for instance, a parallel
> database for
> mail stroage would serve as well.  All sorts of nasty issues-- like the
> security of the data going between the two fileservers, or DBs,
> or whatever;
> significant added latency due to the storage mechanism confirming
> updates have
> propogated; etc appear.

Exactly, this is the wrong way to do this for 80 users.  Now, 80,000
users, that's different.

> My opinion is that it's better to go with a primary mail reader
> box and make
> very certain that box doesn't go down by using redundant hardware
> and a backup
> network link is easier and less likely to suffer from the "lets create a
> complex system with lots of moving parts which never gets fully
> tested and
> thus breaks in some weird way when the unexpected happens" syndrome.  :-)

I concur completely.  The ISP I work at has a heck of a lot more than 80
users and we use a single mailserver as the pop/imap server.  Building a
server that don't go down ain't rocket science.  Building a network that
don't go down is a bit harder, but BGP is for that.  In any case what
with mailservers isn't that the network connection from the server to the
Internet be reliable, what matters is the network connection from the
to the clients that use it be reliable.

If your users are all at one location the mailserver should be there, if
are all across the Internet, colocate your mailserver at a real ISP.


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