Dovecot IMAP server can use a standard Maildir for storage of messages inside user's home directories. The default in that case is to store search indexes and control files in the same directory structure, alongside mail files. That can be convenient, since no special setup is needed and everything is stored in the same place.
However, this doesn't work very well if you have disk quotas enabled on the filesystem that stores Maildirs. In case a user reaches their quota, Dovecot will not be able to write to its own files, which can lead to problems. Hence, documentation recommends that you configure a separate location for Dovecot's files in that case. This is done with
CONTROL options to the
For example, after setting up appropriate directory structure and permissions under
mail_location = maildir:%h/Maildir:INDEX=/var/lib/dovecot/index/%u:CONTROL=/var/lib/dovecot/control/%u
You can just set this up and leave old index and control files in place. In that case, Dovecot will automatically regenerate them. However, this is not ideal. It can take significant time to regenerate indexes if you have a lot of mail. You also lose some IMAP-related metadata, like message flags and unique IDs, which will confuse IMAP clients. It would be better to move existing files to the new location, however the documentation doesn't say how to do that.
I found that the following script works with Dovecot 2.2.13 on Debian Jessie. As always, be careful when dealing with other people's mail and double check that the script does what you want. I had my share of problems when coming up with this. Make backups.
#!/bin/bash set -ue # Run as "migrate_dovecot.sh user path-to-users-maildir" for each user. # Make sure that Dovecot isn't running or that this specific IMAP user isn't # connected (and can't connect) while this script runs! USERNAME=$1 MAILDIR=$2 DOVECOTDIR=/var/lib/dovecot # Correct after double-checking that this script does what you want. MV="echo mv -i" cd $MAILDIR # Index files like dovecot.index, dovecot.index.cache, etc. go under the # INDEX directory. The directory structure should be preserved. For example, # ~/Maildir/.Foo/dovecot.index should go to index/.Foo/dovecot.index. # Exception are index files in the root of Maildir. Those should go under # .INBOX b=$DOVECOTDIR/index/$USERNAME/.INBOX mkdir -p "$b" $MV *index* "$b" find . -name "*index*"|while read a; do b=$DOVECOTDIR/index/$USERNAME/`dirname "$a"` mkdir -p "$b" $MV "$a" "$b" done # dovecot-uidlist and dovecot-keywords files should go under CONTROL, in a # similar way to indexes. There is the same exception for .INBOX. b=$DOVECOTDIR/control/$USERNAME/.INBOX mkdir -p "$b" $MV dovecot-uidlist dovecot-keywords "$b" find . -name "*dovecot*"|while read a; do b=$DOVECOTDIR/control/$USERNAME/`dirname "$a"` mkdir -p "$b" $MV "$a" "$b" done # subscriptions file should go to the root of the control directory. # Note that commands above also move some dovecot-* files into the root of # the control directory. This seems to be fine. $MV "subscriptions" "$DOVECOTDIR/control/$USERNAME"