Outlook cannot connect to the Exchange server. Error code: -18597

I am trying to connect to my company's Exchange server using Outlook 2011 (Version 14.4.8) on my iMac running Yosemite (version 10.10.2).  I can connect fine to OWA by going to webmail.companyname.com and entering DOMAINusername and my Password.  Similarly, I can use the native Mail app on the Mac with no issues to read and send mail.  Within Outlook, however, I am getting multiple error codes, with -18597 being the latest.  I am using the "User Name and Password" method and have provided the full DOMAINusername in the "User name" field.  I have specified the webmail.companyname.com Server in the Advanced window and using the default port of 443.  Any ideas?

Thanks