It looks like my definitions are outside the protocol, as this is the default in /etc/dovecot/conf.d/15-mailboxes.conf...

MUST autoexpunge be declared within the imap protocol, even if the mailboxes themselves are declared outside of the protocol?  Should the mailboxes be declared only within the protocol?

Can I declare autoexpunge for the mailboxes within the imap protocol in 20-imap.conf while leaving the main mailbox declarations in 15-mailboxes.conf?  That is, will the settings "stack" or can mailbox definitions occur only in one place?

If autoexpunge can only be declared within the imap protocol -- folks who access email only through POP (and who never see Junk/Trash) will not have things auto-expunged.  The Junk mailbox, in particular, is auto-populated by spamassassin via procmail so it will have messages even if the user never sees them... so it needs to be autoexpunged even if the user never logs in via imap.

IMHO the setting should apply regardless of protocol, but is that actually the case in practice?

Thanks!

--- Amir