mail crashes every time I try to open it

Press and hold a Shift key while selecting Mail from Applications or the Dock. That action opens Mail with no message selected. Release the Shift key when a Mail message viewer window opens.

If Mail continues to crash, continue below.

Please open  (Apple menu) > System Preferences... > Internet Accounts. Its icon resembles a round blue @ symbol.

In the leftmost column, select the service responsible for your email account. Without revealing your email address, your name, passwords, or anything else you might consider personal, describe what you see on the right side of that window. I realize those instructions may strike you as vague but please describe as much as you can.

At your option, you may post a screenshot of that window but you must obscure the aforementioned personal information because this is a publicly available website in which personal information must never be revealed. Instructions for capturing, editing, and uploading a screenshot to this site please refer to the Appendix in Writing an effective Apple Support Communities Question - Apple Community.