David Mann wrote:

My .pst file keeps getting bigger, despite all folders being set up to
auto-archive.

Looking at the email folders, there are lots of emails still there
that should have been archived. Most of those that are still there
have attachments, and looking in the archive .pst file I see that
there are very few emails with attachments in it. It seems as though
the archiving process usually (but not always) fails to archive any
emails that have attachments.

Keep in mind that autoarchive doesn't work on the Received date. It uses
the items' modified dates to determine if they should be archived.
--
Brian Tillman