[ale] Backup MX basics

[JD]

On 04/21/2014 05:48 PM, 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?


There is a number in the MX DNS record. Primary is lower than 2ndary. That's it.

The synchronization is up to you. I don't bother.  If you make the primary and
secondary only tiny "front-end" servers (mainly spam/AV filtering), then have a
backend-email server to handle all the approved access by end-users (IMAPS (993)
/ authenticated SMTPS (465) only and for outbound email, then you don't have to
worry about synchronization. If the back-end server is unavailable, mail gets
held at the front-end(s).  If one front-end goes down, the other receives mail
still and forwards to the back-end. These front-ends can be tiny - 256MB/2G of
storage.  Simple, easy and the backend server can be located almost anywhere
(perhaps you don't want all email static on VPS storage).

My backups of front-end email servers ignores the actual email - just handles
the list of packages installed and the settings.  120 days of backups is ...
27MB total.

Clearly the back-end email server backups are much, much larger.