best practices for migrating to new dovecot version

[Shawn Heisey]

I have a machine with my mail service on it running Debian Squeeze.  The
version of dovecot on that server is 1.2.15.

I'm building a new server with Ubuntu 18.04 (started with 16.04,
upgraded in place), where the dovecot version is 2.2.33.  I plan to
migrate all my services to this new machine.

The virtual mailboxes are on disk in maildir format, with accounts in a
mysql database managed by postfixadmin.  When I copy them over to the
new machine, would there be any value to excluding the files that
dovecot creates, and letting the new version recreate them?  In one
mailbox here are some of the files I am considering excluding:

dovecot.index
dovecot.index.cache
dovecot.index.log
dovecot.index.thread
dovecot-keywords
dovecot-uidlist
dovecot-uidvalidity
dovecot-uidvalidity.5876ca77

There are other files under consideration, like maildirsize and
maildirfolder.  One that I would be sure to *not* remove is subscriptions.

If there are recommendations about dovecot files in a maildir that
should not be removed during a migration, please let me know.

I'm aware that rebuilding this information could be slow.  My own
personal mailbox on the system is over 8GB in size and has well over
nine hundred thousand files in it.

Thanks,
Shawn