[Dovecot] Denying authentication

Hello,

            I've been running dovecot for over 3 years now and it works

with no problems. I have it setup so that it authenticates users against Active Directory via LDAP and so far no problems.

            What I would like to know is if there is any way that I

could deny access for users trying to access email via cellphones or email clients outside the company. I can close everything since there are a few users that need to get emails from outside the company via cell phone of email clients.

            I was thinking if there was a way to lets say create a group

in AD named: "remote-email" that will allow connection and authentication from any network, any user not in that group will only be able to authenticate if the source is 192.168.xx.xx/24.

Is this possible?

Maybe not with Dovecot, but maybe someone else has any ideas..?

Thanks

Romer Ventura