Message Opening Issue, Outlook.

Hey Team, 

we have one particular user who whenever she responds to a a number of emails (completely random in terms of sender, subject, content) her response cause the recipients Outlook to Freeze. for a period of 3 to 30 seconds each time the message is opened. 

A lot of troubleshooting has been done on this and we currently have a CritSit with microsoft support opened. 

The issue is reproducible 

• By Microsoft support using their own outlook 
• By me when opening up the message in my outlook 
• on a newly provisioned VM 
• On a system (via RDP) to a regular installed (Non vm) Machine

We,re now at the point of using procmon and process explorer to "investigate" but i am curious as to what to look for in those captures? Also outlook logging is enabled, and ETL Files are being reviewed By Microsoft (2nd set). 

I am asking for more of a "What else can be checked" or "How do i check for this in procmon" rather than a solution. (Hopefully Microsoft will provide that). 

Happens on version 2308 and 2401 of Office 365. Windows 10. Additionally if you try to save the messages you get a "Cant save message error" if you try to send the messages outside of our domain, you get a message conversion / bodyconversion error. 

I wonder if this is logical corruption?, Except she can send other emails just fine. 

Thanks, 

Robert