As part of a recent upgrade of my Linux distro, I noticed that deleted messages and mailboxes no longer got removed (expunged or expired). Upon investigation, I reliazed I have to explicitly run a cron job, using cyr_expire, to purge these deleted items. I added the following, which means it'll expire messages and folders that were deleted 2 weeks ago:
01 17 * * * /sbin/cyr_expire -E 3 -D 14 -X 14
For good meassure, I also rebuilt some of the mailboxes, with e.g.
$ sudo reconstruct -r -f -G -V max -u peter