Per the dovecot documentation[0] we were previously running with an
unsupported home directory configuration, because we shared them among
all virtual users at /var/vmail.
After resolving this by creating per user home directories at
/var/vmail/%{domain}/%{user} this now also overlaps with the location of
the Maildir, which is not recommended.
As a result we now need to migrate our Maildirs into
/var/vmail/%{domain}/%{user}/mail, for which a small shell script is
provided as part of this change.
The script is included in the documentation because we cannot provide it
in time for users, because they might already be seeing the relevant
assertion and there is no safe waiting period that would allow us to skip
shipping it like that.
[0] https://doc.dovecot.org/2.3/configuration_manual/mail_location/
With upcoming changes to the dovecot home and maildirectories we need to
introduce a way to nudge users to inform themselves about manual
migration steps they might need to carry out.
The idea here is to allow us to safely make breaking changes and notify
the user of required migration steps at eval time, so they can make the
necessary changes in time.
