[Dovecot] Any simple way to block logins by IP address?

[Steve Campbell]

Does Dovecot have a facility to block pop3 and imap logins by IP 
address. I usually do this by putting the IPs in my border firewall, but 
it's in transition currently to a new one, and I'd like to end 
connection fairly fast.

If it matters, I'm using 2.0.9.

Thanks
steve campbell