Thank you for you thoughts, I have excluded FileMaker, but still have the same problem. I will look into Avast, although this was all fine until I installed 360.
My references to Avast is because Norton v24 is related to Avast.
I am not promoting Avast for you to look into.
Avast users over on Cloris Community report Error 20639 is related to Avast Email Protection.
Norton Email Protection is related to Avast Email Protection.
Avast users over on Cloris Community report turning off Avast Email Protection helps FileMaker.
Did you try turning off Norton Email Protection?..as test.
Caveat: I’m not familiar with FileMaker
Maybe, open a Norton support ticket and offer to send debug logs.