[Dovecot] Limiting Dovecot access by user-spesific ip addresses?

Hi,

Is there any possibility to limit access to mailboxes by user-spesific ip addresses?

So, I'd like to have a configuration which by default restricts reading emails to company's own ip-address range. So far, this could be achieved by a basic firewall rule, but not any more the following:

However, there is need for a few users to access their emails from world-wide internet, so there should be a possibility to define for certain users an option to skip the allowed address range check.

Regards, Timo