Why won't Apple Mail open after install of OS X El Capitan 10.11? Any ideas? I have installed the latest beta of OS X, El Capitan 10.11. The mail app said it needed to index mail. when it finished that process the mail app crashed. Now it refuses to open. Mail has been rendered unusable with this upgrade, for me.

Anyone have any ideas of things I could try to fix this?
Thanks.
I have to remove a PGP plug-in from /Library/Mail/Bundles to get the Mail App running again.

Just open Mail and immediately open Accounts, disable the accounts one by one to find out which one is causing the crash. Then delete this account completely and restart Mail. Then add the account all over again. It worked on my gmail account.