How can I check the OWA (Outlook Web Access)  URL is correct?                 

Sometimes the login page for OWA is different than the actual OWA URL for the mailbox, as redirection may be in place after login.

To check for the correct URL, login in using webmail, once you see the inbox make a copy of the URL visible at the top of the webmail page and then use this URL for Your MM source or destination