[Dovecot] Unresolved client rejection

Hi, would it be possible to prevent users who try to login from an unresolved IP from connecting to Dovecot IMAP? I have a suspicion that it should be done via the authentication module (ie PAM) but I am not sure (if this is the case could someone recommend a good resource or even a solution). For example sendmail has a relevant macro to achieve this, I was wondering if Dovecot can have similar behavior. Thanks