If you setup your POP3 email account in Outlook and you can receive but not send emails, please follow the instructions below:
For Outlook 2003
- Start Outlook, go to 'Tools' and select 'E-mail Accounts...'
- Click on 'Next' then hit 'Finish' to validate the changes
For Outlook 2010
- Start Outlook, go to the 'File' ribbon and click on 'Account Settings'
- Click on 'More Settings...' and go to the 'Outgoing Server' tab
- Check the box 'My outgoing server (SMTP) requires authentication'
- Select 'Use same settings as my incoming mail server' - if not selected by default - then hit 'OK'
- Click on 'Next' then hit 'Finish' to validate the changes.
If following the above instructions doesn't help to fix the issue, please follow this link to entirely review your email account settings.