Outlook hangs for windows 7 machines ever since update

[ddlugose]

We are having an issue that started Last Friday.  When Windows 7 (only) machines are connected to our internal network they can not open Outlook (it hangs).  If that same machine jumps onto an external network its fine.  Also users can run Outlook in Office 365 no problem.   We think some update hit our domain controllers on Friday causing the issue but we have not been able to fix the issue.   We have tried giving user admin rights, disabling our Sophos antivirus but nothing is working.   All windows 10 machines are fine.

[#2]

Check your firewall to see what may be being blocked. Same thing happened to us, had to add exclude certain address before office could load. If i knew what the exact address were i'd list them :\

[#3]

Also, can you confirm your Win7 clients have KB4516551 update installed?

[#4]

@AccotinkCaptain

It looks like it is not installed as its a preview.    You said Firewall.  Are you talking about windows firewall or the Network firewall? 

[#5]

@ddlugose Network