I've got some incoming emails bouncing because they don't have reverse DNS set, so they get rejected like this:
Nov 2 23:18:30 mail postfix/smtpd: NOQUEUE: reject: RCPT from unknown[x.x.x.x]: 450 4.7.1 Client host rejected: cannot find your hostname, [x.x.x.x]; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<mail1.example.com>
I want to receive these, but If I put the IP or name of this server in my whitelist, they still get rejected. Can that be fixed by checking the whitelist earlier? Some other way?
Please have a look in /etc/postfix/main.cf. The reject most likely comes from reject_unknown_client_hostname in smtpd_client_restrictions. You can remove it or add additional whitelists before that if you want. Please post your findings on the mailing list. But it's not a fault as this is how Mailserv was intended to work.