Der E-Mail Server hier ist fehlerhaft konfiguriert bzw. der RDNS ist fehlerhaft. Bitte fixen
Mar 30 18:09:38 [postfix/smtpd] warning: hostname 5-125-236-77.server-home.net does not resolve to address 77.236.125.5: Name or service not known
Mar 30 18:09:38 [postfix/smtpd] connect from unknown[77.236.125.5]
Mar 30 18:09:38 [postfix/smtpd] Anonymous TLS connection established from unknown[77.236.125.5]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)
Mar 30 18:09:38 [postfix/smtpd] NOQUEUE: reject: RCPT from unknown[77.236.125.5]: 450 4.7.25 Client host rejected: cannot find your hostname, [77.236.125.5]; from=<forumadmin@tweakpc.de> to=<mail@example.com> proto=ESMTP helo=<tweakpc4.tweakpc.de>
Mar 30 18:09:38 [postfix/smtpd] disconnect from unknown[77.236.125.5] ehlo=2 starttls=1 mail=1 rcpt=0/1 quit=1 commands=5/6
$ host 77.236.125.5
5.125.236.77.in-addr.arpa domain name pointer 5-125-236-77.server-home.net.
$ host 5-125-236-77.server-home.net
Host 5-125-236-77.server-home.net not found: 3(NXDOMAIN)