Does anyone else have also massive problems to send emails ?
A few of my customers report that they get NDRs that emails specially to 1und1 also gmx also domains hosted on 1und1 came back with "mailbox not found"
other NDR in the HES Log shows :
451 4.4 0 dns query failed smtpsend dns nonexistentdomain
also : an otherone smtp 550 DMARC Sender invalid
I guess its up to 1und1 but not sure it is...
i did not see any problem on the servers or HES. But all customer have the same ExchangeServer and HES. So i appreciate any information if you see something similar on your customers.