I have mostly copied/adapted the setup of the old server to the new. I am in the process of finishing that and adding some stuff that still needs to be added/migrated, like rspamd. And the data of course before the new one takes over from the old.

I have done a migration before (MacOS X Server dovecot to MacPorts dovecot on macOS), many years ago, I recall that I used dovecot syncing but also rsync and I don't really recall (and anyway, the software has changed since)

I have been thinking about keeping them both alive, with one as a failover for the other. They will not share their storage (e.g. NFS), So, I was wondering if I can do something with syncing between instances and dovecot director. I have been looking at the documentation, but a quick scan reveals I cannot locate some sort of tutorial and I am uncertain what will work and what not.

If keeping both alive in parallel is too problematic, it is OK to have regular syncing in one direction (old to new) at first and then switch over and have syncing in the other direction (new to old)

Can someone enlighten me?