Logouts/disconnections not being logged?

[Joseph Tam]

In a previous thread

 	Subject: Re: iPhone/iPad IMAP connection bursts causes user+IP exceeded

I reported the behaviour of MacOSX/iOS IMAP readers whereby it would
use up all available connections (up to the mail_max_userip_connections
setting) for mailbox searches, then log them all out, then repeat the
cycle with another batch of mailbox searches, until all mailboxes were
scanned.

However, login/logout log counts don't square up.  I would observe
(for a particular user+ip) mail_max_userip_connections login entries,
followed by *fewer* than mail_max_userip_connections logout entries.
(I could not find any disconnections or other forms of termination.)

The next peak connection count happened after another
mail_max_userip_connections logins (implying the total connection count
> mail_max_userip_connections), then another strings of logouts fewer
than mail_max_userip_connections.

For example, if mail_max_userip_connections=100, I would see

 	0 -> 100 logins -> 87 logouts -> 100 logins -> 87 logouts
 	-> 100 logins -> 94 logouts -> 100 logins -> ...

It appears that somewhere, somehow, IMAP session exits are not being
logged.  Is there a reason to explain this discrepancy?

Joseph Tam <jtam.home at gmail.com>