Jul  3 11:19:00 bouncer postfix/smtpd[14071]: reject: RCPT from unknown[123.123.123.12]: 530 <qwertyy@domain.tld>: Recipient address rejected: Cannot find your hostname, [123.123.123.12]. Ask your system manager to fix your reverse domain name registration.  If you are sending spam, go away. ; from=<aaaaaaaaaaaaaaaaaaaaaaaaaa@aaaa.aaa-aaaaa.com> to=<qwertyy@domain.tld>