IMAP Idle

[Joy]

Hi guys,
             We have implement imap idle in web mail built by us to have
push mail feature. IMAP idle working perfectly with browser notification
and we are happy with it but having one issue with users who close the
browser directly and never logout in that case there are number of idle
connection which are not in use and users are unable to login once IP wise
connection limit is reached.

Dovecot is not closing connection which are not in use, is there any
setting available which can help me to resolve this issue.