Outlook 2007

I have setup an existing user up on a new PC. This PC is on Outlook 2007. I can receive all new emails and emails still on the server. This is not an exchange server, company uses webmail.us as email client. I can only guess if I have the the setting correct because I can receive all emails just not send. I have read some articles saying I need to contact my ISP and change my smtp setting to their smtp setting and not the one webmail uses. Does anyone know of this to be true, and can anyone help me resolve this issue.