[Dovecot] Replication problem I have. And how I think I can get around problem.

[Peter Dolding]

I have two servers in two different locations.  Neither what you would call
100 percent safe from being turned off.

Most staff use web based email.  This backs onto imap server.   I do know I
will have to deal with contact lists and other items. in that client.

Worst part is the link between them may get broken so both servers may be
receiving email and back active at the same time.

I can see 1 very clear way around this problem.   If I accept that the imap
ids at each of the server will be that server only.

Since users are mostly using webbased they are not going to notice.  If they
do notice because they have connected to a different domain address stiff
bad luck.

Now what I need to be able to deal with the problem.

1 a unique server id on each message for the server the message was received
on.
1 a unique server receive id for each message as imap like id for service
recieved messages for message received directly not synced.
1 logs for messages deleted and changes that are not current server server
id.  This should be pritty simple todo.  Basically 1 log per server flushed
when synced with the server it owns to.
1 a sync function that deletes and changes messages that have been deleted
or changed at other locations and compares other servers current messages
against copies retained at the mirroring location.

Now with this.  Each new message to each store gets the next imap id along
with system wide unique combination of sever id and  service receive id.  No
modifications of already recieved messages ids.   Since I am not careing if
the imap id are matched between servers.

Fairly much able to use a custom for of imap syncing working off the server
id's and server receive ids.

Of course this solution should be fairly fault torrent.  Since each server
can directly store any message they receive.  Also it should be possible to
trace back to what server the message came from in case of spam problems or
equal.

Now my biggest problem can I attach my own custom attributes to incoming
mail to the store and access that information effectively.  Since with that
information I will be able to do a form of live synced storage.

Personally I see imap id design as a defect in protocal since it never
allowed server id along with it this is why imap 100 percent synced message
stores cannot be run on independent servers with unstable network connects
well.

Nothing comes without a price.   This solution does not require clustered
file systems or a constant active connection between servers so able to
operate in areas of disruption.  It does not block the servers from
receiving emails at any time either.

Problem is of course is if someone connects a client directly from 1 server
to another.  Mail will have to be re-downloaded.  Also I have to check of
z-push/ActiveSync  depends on the imap ids being dependable across the
network if not most hand held devices will not be a problem.  If it don't
then only imap has a problem.  I can live with that.  Ie if local email
server down use web mail until local mail server is fixed.

Old rule of networking 40 to 50 percent functional network staff can
normally still get stuff done.  0 percent functional you have downtime.

Now if I can get the email storage fault torrent and to remain operational
in case of fault I then can focus on getting the web base applications using
a equal system for contacts and other things.  So each location can remain
fairly operational no matter what.

This way if a server disappeared for good only thing that would have to be
changed is syncing.  Wise move is to allow servers to be defined more than 1
server id.  Ie a server gone for good remaining server gets told to take
over responsibility for the old servers id messages.  New replacement server
given a new id and everything keeps on going nice.

Anyone else with a better idea or advice how to add my own custom ids in a
way they cannot be distrupted and are simple to search.

If it works push for server id's in imap5?  Ie imap5 clients being able to
cope with the event that an email store is spreed between multi servers that
may not be connected all the time.

Peter Dolding