Mail crashes when opening

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.

Yes that will do it. Check the box only to have it magically un-check itself is one of iCloud Keychain's more endearing features. All I can suggest in that regard is to "sign out" of iCloud, and "sign in" again — the iCloud equivalent of "turn it off and on again". It's annoying beyond reason.

Assuming that doesn't work, try "signing out" and then restart your Mac. Then, sign in again.

If that doesn't work... there are some Keychain entries that can be deleted, but I hope things don't get that far because I'll have to look them up.

Almost certainly, Mail is crashing because it is attempting to make sense of an email protocol it is too old to understand. That problem is going to occur with increasing frequency as more email messages will be composed in compliance with those protocols.

It's all... "for your security" of course 🙄

What you can do: press and hold a Shift key while launching the Mail app from Applications or the Dock.

• That action will cause Mail to open in windowed mode (not full screen) with no message already selected.
• Release the Shift key when the Mail viewer window opens.

In so doing, you may scroll through your email message previews to identify the problematic message(s) and delete them. If that becomes too difficult or tedious to accomplish in the Mail app, at least narrow down the problem to one or a few recent email messages that may be the likely culprits, and then use your email service provider's webmail interface to read or otherwise dispose of them.

Eventually, you're going to need a newer Mac, one capable of running a more recent operating system than 10.11.6 "El Capitan". That's just the way technology goes.

That was going to be my next suggestion 😕 It is possible that old Mail version can't cope with iCloud...?

I have a similarly aged Mac in another office and will see what I can come up with when I get to it.

I am also reasonably certain Yahoo! Mail will be a problem on "older" Macs. They may be going the way of Google, of which I am equally certain.

Same thing with the Shift key?

I was reminded by a colleague the El Capitan Mac I have still works with Yahoo! Mail, so that may be a red herring. So does iCloud Mail. I may have been thinking about Microsoft Exchange mail, which definitely doesn't work. I'll let you know.

Application crashes on macOS can manifest in various ways, including sudden freezes, unresponsive windows, or error messages indicating that the application has unexpectedly quit.

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I have iphone15 and yahoo app is crashing as soon as it opens and reverts to desktop screen. I’ve shutdown and restarted the phone and the app then deleted app and reinstalled.

still crashing. Any thoughts. Thanks.