Why won't Apple Mail open after install of OS X El Capitan 10.11? Any ideas?
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.