LMTP during dsync migration

[Daniel Parthey]

Jogi Hofmüller wrote:
> We are not planning on multiple runs of doveadm backup.  The question is
> what to do with LMTP _while_ the doveadm backup migration is happening?
> 
> At the time when mailbox X get's migrated, the settings used for the
> proxy will be removed, so user X cannot access the mailbox on the old
> server anymore.  Given the size of some of the mailboxes chances are
> quite high that there will be delivery attempts _during_ the migration
> process.  That's what I am thinking about.

What we did was to install a "retry" transport in addition to "lmtp"
in postfix master.cf:

retry       unix -      -       n       -       -       error

See http://www.postfix.org/error.8.html

Before migrating each user, we instructed postfix to route
the affected user to the retry transport. This puts all incoming
messages for this use into the queue while the migration is running.
When the migration of this user has proven to be successful,
you can revert the user to the default lmtp transport.

Good luck,
Daniel