I run Postfix + Dovecot.
Currently, I've got a cloud-instance of Postfix that handles all the
anti-spam/auth/routing.
On successful 'pass', it resends email -- over a VPN link -- to a *local*
Postfix instance, which then LMTP-delivers to a Dovecot instance on the same
box.
Works great.
I'd like to set up some IMAP redundancy, so that if the VPN link is down for
any reason, mail is stored/accessible, and -- eventually -- correctly
(re)delivered to the local Dovecot instance when the link's up again.
The goal state I'm considering looks like:
@cloud
Postfix
LMTP delivery from Postfix to "Dovecot1"
@local
LMTP (re)delivery from "Dovecot1", @cloud, to "Dovecot2"
IDEALLY, no IMAP mail should ever be persistently stored on the @cloud Dovecot
instance -- unless the VPN link is down.
Then, when the VPN link is up again, the @cloud-stored IMAP mail should me
'moved' to the @local instance.
I.e., I do _not_ want a replicated store.
My question is how transparent/automated can this be done?
I'd guess that somewhere in Dovecot's config I need logic that provides the
conditional delivery to just @cloud vs 'all the way' to @local ...
Any suggestions as to how to put this VPN-conditional redundancy in place?
