I have an old server with CentOS 6.x and dovecot 2.0.16 (postfix-2.6.6 and roundcube), that was an update from a 1.x many years ago ... Users in /etc/passwd Mailbox format mbox some filtering via procmail About 5.000 users, 1 TB data (/var/mail + /home/users)
Obviously I am searching for a smooth upgrade path (with no or minimal downtime and users problems) ;-)
Until few days ago my idea was a CentOS 8.x new box with the standard default packages (dovecot-2.3.8, postfix-3.3, ...). Now this can be reconsidered. I suppose there will be a RockyLinux or something equivalent but if there is a good reason I can consider Debian or other OS if they have a decent EOL or some advantages.
Anyway, the more relevant problem at the moment is collect info for the best approch to have a smooth dovecot upgrade.
My dream is the possibility to configure a new server and rsync the data (/var/mail + /home/users), and, when the tests are satisfiable do the final sync and swap the IP, but I suppose deleting the .imap folders isn't a simple complete solution to compatibility problems.
Any hints, links, experiences are appreciated.
Thanks, B.