I explicitly added
reject_unknown_client_hostname and several other reject rules to slow down SPAM in our server. So far that's working nicely.
However, there is an important client that keeps getting rejected by our mail server, either because there isn't a ptr record on their name server giving a valid hostname or because dns lookups are failing.
warning: 00.00.00.00: hostname 00.00.00.00.dynamic.isp.com verification failed: Name or service not known
In any case, before they get that fixed with their ISP, is there a way to allow only their IP in our postfix? I tried adding it to
mynetworks but it didn't work.