How to fix the problem:
- In Outlook, go to "Tools" and select "Email Accounts". Make sure "View or change existing e-mail accounts" is checked.
- Click Next.Select your account from the list and click "Change".
- Select "More Settings".
- Select "Outgoing Server".
- Check "My outgoing server (SMTP) requires authentication".
- Make sure that Use same setting as my incoming mail server is selected
- Click "OK", then "Next", then "Finish".