ronaldst wrote:
The recipient webmaster@anotherdomain.com is a valid email account/user on mx.mailserver.com (iRedMail).
I suppose you use "postmaster@mydomain.com" as smtp authentication user while relaying, isn't it? Why it shows "root@mydomain.com"? If the 3 log lines are not the FULL log related to this mail session, please paste full log for troubleshooting.