Since I installed El Capitan, I have been completely unable to open Mail.app. I've removed all my email accounts, I've removed all the file in the MailData folder (even the Accounts.plist) file. Nothing works. As soon as I open the app, it shuts down and I get an error message of

    Application Specific Information:
*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<HeadersEditor 0x7fcadc585410> valueForUndefinedKey:]: this class is not key value coding-compliant for the key _documentEditor.'
abort() called
terminating with uncaught exception of type NSException

Has anyone else experienced this? What can be done? I don't want to have to do a fresh install of the OS...

1 Answer 1


I've had the same issue and found that I've had an incompatible version of GPGMail installed. Removing the files in /Library/Mail/Bundles fixed it for me.

  • That was it! I removed GPG and it opened backup.
    – Delmania
    Oct 2, 2015 at 18:09

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