Can't send email wireless in Office 2007

I'm in a POP3 enviornment where my email server at work requires user /password authentication which i've enterend into the Outlook profile setup for the user. now when the user is logged into the network via network cable he can send / retrieve emails just fine.
when the user goes wireless he can retrieve but can't send.
Under the "Outgoing Server" tab under the window "Internet Email settings," i would have to check "My outgoing server (SMTP) requires authentication" and enter my username / password. then it will work fine.
if i go back to my office network then i can't send email out i would have to go back to the same sreen Under the "Outgoing Server" tab under the window "Internet Email settings," and uncheck the box for "My outgoing server (SMTP) requires authentication" .
any ideas on how i can have it work when i'm wired into the network then when i'm wireless.
Note: Under Outlook 2003 it worked fine, but in Outlook 2007 i'm having this problem.
THanks.
Bill