outlook 2003 not sending email

This is driving me nuts. :cry
I can receive email but I can't send it. If I log onto my servers webmail account I have no problem sending email but if I try to send it thru Outlook 2003 or Outlook Express 6 it doesn't work. This just started within the week and the only odd thing that I had was a pop up that would come up stating - (Enter Network Password) and asking me to type in my user name and password. I would click the X because I wasn't sure why it was coming up and didn't want anything to be changed.

Things I've tried:
unchecking - My out going server (SMTP) requires authentication
checking - Log on to in coming mail server before sending
checking - Log on using Secure Password Authentication (SPA)
Telnet connection is okay
Checked that my Firewall was allowing Outlook (Shut it down to make sure)
Check Virus software was okay (Shut it down to make sure)
I'm running Windows XP SP2
Please help

 

What kind of mail server do you use? Exchange or internet mail? To me it sounds like a corrupted profile in Outlook. Profile i closely connected with the services and protocols used to send and receive mail.

 

Did Outlook Express previously work? Did both Outlook and Outlook Express previously work? Have you visited your ISP's website (assuming your email account is with your ISP) to see whether they've made any change to the POP or SMTP coding or other setup elements?

 

Have you changed isp's recently? Are you traveling and on a different connection then normal? Both of this may require you to change your outgoing smtp server to who ever is providing your current connection.