Mail crashes when sending
I upgraded to El Capitan when it came out. And everything was fine. Now all of a sudden Mail crashed every time I opened it. Looking at other support discussions I deleted the "envelope" files and reopened Mail without crashing. However, it does crash every time I try to send email from any of the accounts I have. Disabling all my accounts and starting with any of them still results in an instant crash when I try to send email regardless of the account. BTW of course I've rebooted my MacBook Pro too. Any suggestions?
Here's part of the error report:
Process: Mail [19359]
Path: /Applications/Mail.app/Contents/MacOS/Mail
Identifier: com.apple.mail
Version: 9.0 (3094)
Build Info: Mail-3094000000000000~1
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: Mail [19359]
User ID: 501
Date/Time: 2015-10-12 11:36:37.836 -0400
OS Version: Mac OS X 10.11 (15A284)
Report Version: 11
Anonymous UUID: 3A587A72-7303-821A-9B94-2E44DE20D751
Sleep/Wake UUID: FEEA9B2B-CC15-4841-A023-E6383D9BAFE1
Time Awake Since Boot: 17000 seconds
Time Since Wake: 3200 seconds
System Integrity Protection: enabled
Crashed Thread: 19 -[DeliveryQueue _deliverQueuedMessages:] Dispatch queue: NSOperationQueue 0x7fefa94c6d30 :: NSOperation 0x7fefaed3b770 (QOS: UTILITY)
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MCMessageHeaders removeHeaderForKey:]: unrecognized selector sent to instance 0x7fefaed531f0'
abort() called
terminating with uncaught exception of type NSException
MacBook Pro (15-inch Late 2011), OS X El Capitan (10.11), Mac Mail