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