Mail refuses address with "dots"


We use Mail 1.3.11 in MacOS 10.3.9 here at the office. I have problems when sending mail from one client. The program sometimes refuses mailaddresses, says they are not valid. These are addresses that work for other users, and on other mail programs. Usually it's addresses with more than one "dot" in the name, like "" or "".
The mail account is configured exactly as all the others and the prefs are the same as all others.

Please help!
Can't confirm. Both and always work for me in - any version. However if you happen to have a rogue space character (might not even see it at first sight...) or something else sees as "not good" (rightfully so, I might add...), you might _think_ it's the dots, but isn't.
You are correct, "dots" works for me too, and everybody else at the office, except for one in computer. Yes I have checked for rouge characters like spaces and stuff.
Hope the problem disapperes when I upgrade to Tiger.