Outlook connects to the incoming server but will not send emails:
Please make sure that you have the checkbox for ‘My outgoing server (SMTP) requires authentication’ checked for this account.
You can find this option by clicking:
1. Tools > E-Mail Accounts > View or change existing e-mail accounts
2. double-click the relevant email account then click ‘More Settings…’
3. then the ‘Outgoing Server’ tab.
This applies to Outlook, however Outlook Express is similar.