OT: Backup MX

[Jon Radel]

Green, Rodney wrote:
> 
> 
> 
> Green, Rodney wrote:
>>
>>
>> Green, Rodney wrote:
>>>
>>> Hello,
>>>
>>> We recently had a day of downtime for our Internet connection. We
>>> don't have a backup MX to queue mail while our  mail server is
>>> unreachable.
>>>
>>> My question is this. If I were to get a DSL connection setup and
>>> connect a backup DNS server and backup MX server, would there be a way
>>> for users to access incoming mail that is queued on the backup MX?
>>> How is something like this normally handled? We rely on e-mail here and
>>> need some sort of backup plan if our main connection goes down.
>>>
>>> Thanks for any suggestions.
>>> Rod
>>>
>>>
>>>
>>
>> Just to add a little more information.. I'm using postfix as our MTA
>> and of course MailScanner.
>>
>>
>>
>>
> 
> Replying to my own post yet again. :-)
> 
> I think my answer is in how DNS and MX records work. I guess I was
> confused by the term "backup mx." It looks like I would need to setup a
> duplicate mail server on the DSL connection, with a different FQDN, of
> course, and set it up as a final destination for mail. Then in DNS I
> would set up that new server with a lower priority than the normal
> server. If the primary server is down mail should then be delivered to
> the server on the DSL connection and be accessible to the users with a
> simple configuration change. Does this sound correct?
> 

No.  It sounds like a horrible mess.  Manually maintaining the same
users on two independent servers.  A single user's mail split across two
servers, with where a piece of mail sits depending on connectivity
between the sender and your servers (your "backup" server would get some
e-mail even if your main connection was nominally up, and it wouldn't
*all* be spam).

Easiest of all would probably be buying one of the turn-key boxes
available that allows you plug in multiple ISP connections and handles
all the connectivity tracking and fiddling with multiple NAT tables for
you.  I suspect they come with explicit hints on how to setup your MX
records to interop with their box.  (I'd give brand names if I could
recall any at the moment.)

Probably second easiest would be to simply multi-home your SMTP server,
with an address from each ISP.  It would then accept connections across
either connection.

Another possibility would be to actually have a backup MX server, but
make sure it could reach your mail server across a LAN connection so
that it could forward incoming mail.  This one wouldn't help with the
problem of off-site clients reaching the server across the Internet.

Lots of choices, many of them driven by factors you've not covered here.

--Jon Radel