[SA-exim] synchronizing tuplets between multiple mtas

[Marc MERLIN]

On Wed, Apr 20, 2011 at 11:57:57AM -0300, Jeremy Hockin wrote:
> I'm looking to deploy SA-exim with intelligent greylisting to one of my
> mail environments that runs with 2 exim mtas screening and relaying mail
> to a windows mail server on the same LAN.  They are using round robin
> dns to "load balance" incoming and outgoing mail but this generates a
> problem when using greylisting.  I am using sa-exim with greylisting in
> another environment with a single mta and really quite pleased with it,
> but the round robin dns makes this dangerous for the 2 box setup.  My
> thought was using something like unison to keep the tuplet directories
> synchronized in real time between the two exim boxes.  Does this sound
> like a recipe for disaster or a proper method to accomplish this.  The
> two exim boxes are on the same LAN and run identical exim configs.  

I would indeed use something like rsync or unison: 
- you don't have to propagate deletes, so it's easy, each new file is copied
  on the other side.
- it's not a big deal if you overwrite one file with another one of the same
  name but slightly different data in case the same tuple was created
  independently on both sides.
- replication does not have to be instant: greylisting is supposed to tell
  sender to go away for a while, so you have up to one hour to replicate
  the missing tuples.

In other words, I haven't done this myself due to lack of need, but I don't
see this being a problem.

Also, if you only have 2 servers, you don't actually need to replicate: you
can just let the sending server try both your MXes and on the 3rd time, if
at least one hour has passed, it'll go through.

Marc
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Home page: http://marc.merlins.org/