Outlook can’t send after upgrading to Windows 10

I just upgraded to Windows 10 and now Outlook can’t send anymore. All the mail server settings are correct and interestingly enough, the test message is successful as well. The error message I get it;

Error message: ‘Robert – Sending’ reported error (0x800CCC13): ‘Cannot connect to the network. Verify your network connection or modem’

How can I get sending back to work again?