To enable SMTP authentication within windows mail, try this:

1. Go to "Tools" > "Accounts"
2. Select "Properties" after selecting the appropriate account
3. Select the "Servers" tab
4. Check the "My Server Requires Authentication" checkbox, and select "Settings"
5. Within the "Settings" page, confirm that the radio box "Use same settings as my incoming mail server" is selected, and hit "OK"
6. Close the rest of the screens

Everything should now work. If you're still having trouble, get in touch!