Dovecot expunge with POP3

I want to have Dovecot remove e-mails from a POP3 inbox that are over a year old, regardless of whether they have been read or not.

From what I have read for autoexpunge to work the message should be marked as deleted. Not only would that seem to rule out POP3 as POP3 wont add any delete flag (as I understand it). But it also means if IMAP were used a user leaves a full inbox without deleting e-mails then nothing can get deleted.

This page seems to offer a partial solution for IMAP boxes but it doesn't look like that would be practical for many domains, I want this to work system wide.

https://dovecot.org/pipermail/dovecot/2015-December/102776.html