Mail crashing in Big Sur

I have an other problem: Mail doesn't work anymore !!!!! I cannot receive any mail anymore. Sending mails work. I have different mail account. Same problem with all mail accounts. I did not change anything in the settings. Only updated to Big Sur today afternoon.

After installing Big Sur 11.0.1 - Apart from crashing randomly, all my flagged emails are gone respectively the flags... There were random emails visible under Flagged and after clicking on the flag colors all disappeared, now there is 0 flagged email...

In general, the system crashes also after some time without exactly knowing which program caused it.

All of a sudden Mail wouldn’t even open although it knew it had Mail.

Lost all my Mailboxes with all my emails.

Apple Support Senior Adviser spent over 1 hour with me. A real hero! She finally got my email back again in a very new looking email layout. Unfortunately can not retrieve all my mailboxes back with some very important receipts and records. Has been escalated to Apple Engineering so the can resolve the issue.

I have got time machine however the issue is complex so if I do back up it may not have the correct platform to land on.

This has to be Big Sur update. What a nightmare!! Trust Apple will resolve this very soon!

Go into internet accounts on system and turn off icloud mail. Then the mail quits using 365% cpu and freezing everything.

All the other mail accounts work fine. I will have to use my ipad or iphone to access the icloud saved items in many folders.

My Mac Mail was working when I upgraded to Big Sur for a few weeks. However, today is froze when I would simply enter in an email address. Turning off "iCloud" mail as suggest above fixed the problem. (for now)

Thank you!

A solution I found on my end was to force quit "deleteMailCache" in Activity Monitor. My mail would refuse to open, display full screen, or show any windows. It was barely responsive and the mouse wouldn't work on it despite restart efforts. The problem wouldn't go away until I tried this. Hope it helps anyone looking for an alternate solution.

Turn off iCloud mail tried but not working on my side. I still have lot of mail app crashing and impossible action (like moving emails form email boxes to other one, restaure spam to received box...).

I've found that if I wait 15-20 minutes after a reboot to launch mail, it works fine. There is something about starting it up too soon that makes it hang.

Apple - what the heck could take that long on a 16 core pro tower???

Same here - find my Mac Pro experience really testing ... bad enough that my screens show super annoying graphic bugs like buttons disappearing in Music.app but now my Mail.app is basically useless. It only works when i disable the exchange account. Deleting the Mail folder in the user profile helps for 1-10min. From then on it immediately crashes when startet again. Feel like quality control at Apple took a hard dive.

I also had this problem with Mail (frequents hangs upon start, also the search function did not work properly), so I reinstalled Big Sur and now it seems to work fine... So until thse issues are fixed in an upcoming update, a new copy of Big Sur to be reinstalled might help, I guess...

Does the problem also occur if you restart in Safe mode (hold the shift-key while restarting until you see the Apple-logo)? Rebooting in safe mode can take several minutes.

I am having same issue.

I tried it in Safe Mode and it did not crash. Rebooted back to normal now it does NOT crash. Strange.