Resolved Mailserver Postfix not sending Mails to GMX

[Matje M]

Hello

I am using Postfix as Mailserver on Plesk and I am facing the issue that registered Mails can not send to certain providers such as GMX.
After some days they get a message back thtat the mail could not be delivered due to the following error:

host mx00.emig.gmx.net[212.227.15.9 refused to talk to me:
554-gmx.net (mxgmx013) Nemesis ESMTP Service not available 554-No SMTP
service 554-Bad DNS PTR resource record. 554 For explanation visit
Error messages | GMX Postmaster​

It says Bad DNS PTR record but if I test it on MX Lookup Tool - Check your DNS MX Records online - MxToolbox for example everything seems to be fine.

How can I solve this problem?

Thank you

 

[Bonsai78]

Did you check the DNS entry also by asking the DNS servers of GMX? If their own DNS server is not working properly, then you get this issue, even if you configured everything fine on yours.

You also read the third point?

Individual rejection of the PTR-RR for system protection reasons. Please contact the administrator of your system who should then contact us.

It might be, you are just blocked by them.