I used Eudura and it works fine. I prefer Outlook though....called my ISP and they said it was my problem not theirs. It is real sporatic, sometimes I can forward, sometimes I cannot.
Is the problem as simple as you are typing in the address wrong? Or that persons email has been shut down? I am in charge of a list serve at school here with about 40 people on it and every once in a while I will get an email like that saying that either the persons inbox is FULL or that address is no longer existant. That could be the same problem....