Setting due date while e-mailing to board

I'm trying to find a way to set a due date for a card in the process of e-mailing it to a board. Our organization will not permit us to activate the AI summary that would identify a due date in the body of a message, and I can't seem to get this function to work in setting up an automation. I was trying to accomplish this by adding a due date in brackets [ ] in the subject line. The rule currently set up reads: when I enter a card name containing a date after "[", set due on the date and remove the matched text."