[ale] Backup MX basics

[Horkan Smith]

Please note, this is *NOT* a good idea anymore unless you have full control of both the primary and the backup MX.  Both mail servers need to have an identical idea of when to accept or reject a given email, or you'll become a backscatter spam source.  (Says the embarrassed admin of a former backscatter spam source....)

Honestly, the vast majority of mail servers that would send you email will hold it for a reasonable time (I think 5 days, might be wrong.)  I've mostly found it
 usefull for the rare case that I'm down even longer, or if I need to dig throug
h the mail spool files for that one special email that came in while my main ser
ver's down.

As JD said, set up another MX record on your DNS server.  It should have a larger number (lower priority) than your main MX server.  My primary is '10', first backup is '20'.

Configure your backup MX server to 'relay' (not accept) mail for your domain - it'll then accept it and forward it.

You can configure the backup server to follow whatever retention policy you feel comfortable with.

Mail senders that follow the rules will see your primary MX record, and try to send it there.  If that doesn't work, they'll try your secondary.  Your secondary will accept it because you've added your domain as a relay destination, then itwill start trying to send it to your primary, and will keep trying until it works, or the email expires.

Mail senders that don't follow the rules (spam senders, among others) will pick on your lower priority MX records first, 'cause they figure they're less likely to get rejected.

later!
   horkan

On Mon, Apr 21, 2014 at 02:48:50PM -0700, Alex Carver wrote:
> I'm was pondering a backup MX for my server (I still haven't fixed its
> clicky IDE drive) but it occured to me that I don't actually know how a
> backup is configured to A) be the backup and B) make sure that it
> delivers/synchronizes mail to the primary eventually.
> 
> Searching around online hasn't quite given me the basics, it just gives
> me configuration parameters for different daemons without a full
> explanation.  For example, I would assume that a backup has a more
> liberal delivery timeout (e.g. ten days instead of four) but nothing
> I've found makes any of that clear.
> 
> Suggestions for things to look at or just personal experiences?
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-- 
Horkan Smith
678-777-3263 cell, ale at horkan.net