Why does my email close randomly?

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

If still no good Disconnect from the Internet, then start Mail, look for the last rec'd eMail.

Does Mail crash if no internet?

Quit Mail & login to your WebMail in a Browser, if possible delete any later eMails there after the last rec'd one on the Mac.

If you have no POP accounts & they’re all IMAP accounts then in Mail’s Mailbox menu choose Rebuild.

i do not understand the acronyms POP vs. IMAP accounts can you explain ?

I can't open mail for more than .5 seconds even in safe mode. desperate for help I've run diagnostics cleaned caches and RAM

need help

If still no good Disconnect from the Internet, then start Mail.

Does Mail crash if no internet?

The original protocol is POP. It was created in 1984 as a means to download emails from a remote server. IMAP was designed in 1986 to allow remote access to emails stored on a remote server. Essentially, the main difference of the two protocols is that POP downloads emails from the server for permanent local storage, while IMAP leaves them on the server and just caches (temporarily stores) emails locally. In other words, IMAP is a form of cloud storage.

https://www.makeuseof.com/tag/pop-vs-imap/#:~:text=Essentially%2C%20the%20main%20difference%20of,a%20form%20of%20cloud%20storage.

Any luck yet?