I am working with a remote server (Windows 2012 R2 64-bit) where our remote employee log into a virtual desktop via Remote Desktop Connection. We are on Filemaker Pro 16 (32 bit) and O365, Outlook (32-bit) every thing seems ok and working fine. Then all of a sudden it start giving us "unknown error: -1" message when we go to send an email from Filemaker. If you close Filemaker and Outlook it start working again for 1-6 times before it happens again. No one that is able to connect to the Filemaker Data from a PC/MAC do not have this issue.
I have looked at the setting on the server and PC and Filemaker and many of the Office setting and they are the same. I can seem to find why this is happening.