Mail quits precipitously after opening (under MacOS 27.01)

Mail quits when I try to open it (under MacOS 27.01). I reinstalled the system, but the unsolicited quit continues. Upon retrying, a window opens informing that windows could not be closed because of the precipitous quit, and asking whether to open them or not. Whatever one chooses the unsolicited quits continue. My mail works normally on the iPhone, the iPad and une Microsoft Outlook. The value of Mail under MacOS is access to a very extensive folder system with access to my exchanges with a variety of other researchers and lists over many years. Any suggestions as to how to lift the blockage?