IMAP Idle

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.