554 Bad PTR Record but Record exists and is correct

ptr-record email-server

The remote mailserver thinks you are coming from a dialup connection with a dynamic IP because of the format of the reverse DNS pointer with the encoded IP and rejects the connection.

We had the same problem with a VPS at HostEurope. That seems to be a heuristic to fight spam that United Internet started using rather recently.

To work around this, change the reverse DNS PTR for the VPS to point to your own domain in the HostEurope control panel: https://kis.hosteurope.de/administration/ip-netze/index.php

See also https://faq.hosteurope.de/?cpid=11518 (German)

Of course, you can also try to convince United Internet to adjust their heuristic or wait until somebody else does. But this will probably take some time.

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