Do you mean disable Edit Message option under Action menu?

According to my research, we can add Control ID 5604 to disable “Edit Message” option. I’ve tested this on both Outlook 2016 and office 365 pro plus.
Please refer to following screenshot:
Administrative Templates > Microsoft Outlook 2016 > Disable Items in User Interface > Custom > Disable command bar buttons and menu items

(If you don't see Microsoft Outlook under Administrative Templates, you need to install templates first.
Check this link)
Hope the information is helpful to you.
Regards,
Perry
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