I have reported that some of my users can't send email to a few of mail server. While they have no problem to send email to others domain.
Error transferring to in.mx.skynet.BE; SMTP Protocol Returned a Permanent Error 451 4.1.8 Domain of sender address email@example.com does not resolve
The strangest thing is that the return error firstname.lastname@example.org, while our server should be domino.domain.com.
All clients registered to our DNS server automatically everytime the have IP from DHCP server.
Our domain is valid, and also have PRT record for domino.domain.com