actually not
but we discovered, that somehow inheritation was disabled by this user; when i enabled it via my workstation (mmc) it looked like everything was ok, but after a short time, my made settings were resetted. When i changed the settings via logon at a domain-controller i discovered that these settings were not resetted any more.
This was the problem, now he's able to send

, but i think his AD-User is bugged

thanks for the replies anyway
kind regards