Exceptions to reject_invalid_hostname ?

[Frank Bonnet]

Hello

I have the following rules in main.cf :
smtpd_recipient_restrictions =
   reject_invalid_hostname,
   reject_non_fqdn_sender,
   reject_unknown_sender_domain,
   reject_unknown_recipient_domain,
   reject_unauth_pipelining,
   permit_mynetworks,
   reject_unauth_destination,
   reject_unlisted_recipient,
   check_policy_service inet:127.0.0.1:10023,
   permit


I wonder if it is possible to add exceptions to the 
reject_invalid_hostname statement because two professors
need to receive some emails from few persons that haven't
well configured machines and don't have DNS access/knowledge.


Thanks a lot