Below article will show you how you can enable SMTP authentication for Microsoft Outlook 2007
Microsoft Outlook 2007
1. Open Outlook
2. Go to Tools -> Email Accounts
3. Select the Account with the trouble and click Change
4. Click on More Settings
5. Click on Outgoing Server Tab
6. Click "Outgoing Mail Server (SMTP) requires authentication" and make sure "Use same settings as incoming mail server" is checked.
7. Click on Advanced Tab
8. Set outgoing Port (SMTP) to 587 or 25 for NON SSL type and 465 for SSL type
9. Click OK and then Test Account Settings.