How to set the Due Date By field or custom Due Date Field from Email Command

How to set the Due Date By field or custom Due Date Field from Email Command

I have followed the example from the help file without any luck 

@@Due Date=22 Nov 2021, 10:30:00@@    ---****Custom field***

@@DUEBYDATE=22 Nov 2021, 10:30:00@@

Nothing is working any help?