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Leider verweigert t-online.de den Empfang von Mails von manitu.net. 

Bitte um eine Lösung.

Hier die NDN Nachricht ( anonymisiert)

Von: Mail Delivery System <MAILER-DAEMON@ngcobalt404.manitu.net>
Gesendet: Sonntag, 24. Juli 2022 08:48
An: XXXXXXX
Betreff: Undelivered Mail Returned to Sender

This is the mail system at host ngcobalt404.manitu.net.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.

The mail system <XXX.NNNN@t-online.de>: host mx00.t-online.de[194.25.134.8] refused
to talk to me: 554 IP=89.238.73.104
A problem occurred. (Ask your postmaster for help or to contact tosa@rx.t-online.de to clarify.)