[Dovecot] pop3_lock_session question

[Justin Krejci]

> > > Why doesn't this happen with imap?  Why can't we make pop3 do what
> > > imap does?  Even if it's inefficient, it's better than hanging all
> > > incoming mail delivery while deliver eats up our local concurrency
> > > limits.
> >
> > IMAP unlocks mbox after each command is done. But POP3 clients typically
> > just run RETR, RETR, RETR, .. so unlocking + locking again later is just
> > extra work that slows things down. I guess there could be a timeout that
> > if no RETR has been run for a few seconds it unlocks the mailbox.
> >
> > But I've never before heard POP3 clients behaving that way, so I'd like
> > to know what exactly are they doing. Are they not sending anything? Are
> > they NOOPing? I don't see any reason for them to be doing either..
>
> In the cases I've looked into, the client seems to be connected and
> not doing anything.  I don't have access to the clients or end users,
> but ktrace on the pop3 process basically is producing no output or
> very little output over an extended period.

> Could it be an interactive client which maintains an open pop
> connection, even when no one is actively doing anything with it?
>
> The "unlock after a few seconds" option would be great.
>
> Do you have any documentation or hints on how to identify or debug
> connecting pop clients without involving the end user?


Could it be some (older?) webmail clients that use pop3 instead of imap?