Hello!
I have this error message when I try to send an email to certain domains. Already tested it with another e-mail service as a google account and I get no error message and is delivered successfully, but unfortunately not my domain.
With the other addresses i can send and receive the e-mail's without problems.
Undelivered message:
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.
theemail@thedomain.pt Invalid Address, ERROR_CODE :550, ERROR_CODE :Verification failed for <myemail@mydomain.pt>
Unrouteable address
Sender verify failed