Kann das Problem auch beim Empfänger liegen ??
5.X.X Permanent Failure A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery. X.5.X Mail Delivery Protocol Status The mail delivery protocol status codes report failures involving the message delivery protocol. These failures include the full range of problems resulting from implementation errors or an unreliable connection. Mail delivery protocol issues may be controlled by many parties including the originating system, destination system, or intermediate system administrators. X.5.0 Other or undefined protocol status Something was wrong with the protocol necessary to deliver the message to the next hop and the problem cannot be well expressed with any of the other provided detail codes.