Can Dovecot honor Outlook's "leave mail on server for X days" setting?

[@lbutlr]

On 03 Mar 2021, at 00:19, Joseph Tam <jtam.home at gmail.com> wrote:
> On Tue, 2 Mar 2021, Steve Dondley wrote:

>> I've got a linux box running dovecot/postfix using maildir format. I
>> was surprised to learn that a client that had many GBs of email was
>> running POP3, not IMAP. It turns out they had a setting to delete POP3
>> mail after X days turned on but it just went ignored.

I turned off POP3 support nearly 20 years ago. I only allow it for users who are importing their mail into gmail (though in theory I would allow it for other users who wanted to import into some other service, assuming it worked). Gmail I know will removed the messages when they are retrieved, so I do not have to worry about broken MUAs.

>> I know this is not how POP3 is supposed to work, but is there a way to
>> get dovecot to honor the user's settings in Outlook? Or should I just
>> tell the client to turn this off and use a proper IMAP account?

As Joseph says, this is a MUA setting and is controlled by the MUA.

Of course, you could do things like move all messages from the inbox after 30 days to the archive mailbox and auto-expunge your user's Junk and Trash folders, but that will duo little with a POP3 user. Best to simply tun off POP as far as I'm concerned.

I do offer a roundcube (used to be Squirrelmail before it was abandoned) for those people who still claim they do not have a MUA that support IMAP.

> It's not dovecot (or any POP3) server's job to implement this setting, it's
> the client's.  Typically, the mail reader downloads a list of messages,
> then issues "DELE" commands to remove messages based on whatever criteria
> the user had set.  Dovecot has no idea what the user's setting is.

POP3 is a "feature" that is included in modern MUAs just because it always has been. There is no reason to use it and it offers no advantages over IMAP and many disadvantages. Your user's POP stack was probably last looked at by a competent programmer early in the 2000s.

Turn it off.

(Users can connect to my mail server on ports 993, 587, and 465; and only on those ports, using TLSv1.2 and 1.3 only. If their MUAs cannot handle that and they will not upgrade, they can use the webmail or gmail).

-- 
'Why?' he [Rincewind] said. The world is going to end. 'What, again?'