I was somewhat apologetic about the lack of delete-after-N-days
features in Linux mail clients, since my mom relies on that to keep
mail volumes manageable and yet still be able to share mail with other people.
Then a message on debian-user@lists.debian.org alerts me to the fact that
some people use something like this in their crontab:

» #  m   h  dom mon dow command
» # auto archive debian-user messages over 14 days old
»    40  8   *   *   *  archivemail -q -d 14 —delete imap://mrroach:password@okmaybe.com/INBOX.debian-user

I’ll install archivemail on the Lifebook and see if it does the work…