Cannot Login Through Webmail ( Squirrelmail )

I have having some issues with sending/receiving email. I have the following running on my linux virtual dedicated server with godaddy:

Postfix
IMAP
Squirrelmail(webmail)

My problem is: I can logon through webmail using the domain account but I cannot logon using any email accounts I created. I can also send emails out from the server from the command line i.e.:

root@myserver.com# echo "test" | mail -s testsubject someemail@hotmailorwherever.com

So instead of using webmail, I tried using OUTLOOK and experienced the same issue. I can logon using the domain/system account but not any using any of the email accounts i created using simple control panel.