Re: [exim] EXIM as bacup MX vs SPAM

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Author: Tony Finch
Date:  
To: Giuliano Gavazzi
CC: exim-users, Agusti
Subject: Re: [exim] EXIM as bacup MX vs SPAM
On Fri, 27 May 2005, Giuliano Gavazzi wrote:

> I'd like to do that too.. there is one problem though. I use IMAP, of course,
> so messages are left on the server. The problem is that you want to maintain
> some consistency, and allow deletes at least on one server, say the "primary".
> Supposing the "secondary" only allows modifications to the "sent" mailbox, so
> that sent messages can be saved there, what happens when the user deletes
> messages from the "primary" server? How do you propagate those to the
> "secondary"? And how do you synchronise the status?


You can't perfectly replicate a mailbox with pure IMAP because it doesn't
allow you to set metadata like message numbering. This is why our mail
system uses a custom protocol for replication. It's a one-way replication
mainly aimed at providing a live backup - i.e. not load balancing. The
latter needs two-way replication which is much harder from the conflict
resolution point of view. This stuff should be appearing in the standard
Cyrus distribution soon.

http://www.cus.cam.ac.uk/~fanf2/hermes/doc/talks/2004-02-ukuug/

Tony.
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