Apple Mail app keeps loading windows attempting to send emails

I almost never use the Mail app and find it very annoying in general. Often times it will automatically load if I click on something like an EML file. Now, when it loads, thousands of windows are loading up, one after another -- they appear to be very very old emails I sent. They load with an error, "cannot connect to sending mail server" or something. But by the time that error appears, then another window pops up with the same error. It is a nightmare where I am unable to close these windows or stop the endless pop-ups. It also hijacks my ability to do much of any settings/config fiddling in the Mail app itself. I also know that eventually my system would run out of memory. So I am forced to "Force Quit" from my system dropdown. But those windows will all auto-open if I accidentally open the Mail app again. Please help me [1] delete the root cause without opening the Mail app to do so; [2] delete this useless, oppressive application, forever.