My Yosemite Mail app crashes similarly (that is, with an NSRangeException), when some emails are selected. I have switched off the IDLE option on the accounts, which made no difference, and removed plugin bundles, which also made no difference.
The top of the crash report is as follows:
Process: Mail [7264]
Path: /Applications/Mail.app/Contents/MacOS/Mail
Identifier: com.apple.mail
Version: 8.0 (1990.1)
Build Info: Mail-1990001000000000~3
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: Mail [7264]
User ID: 501
Date/Time: 2014-11-05 11:42:32.504 +0000
OS Version: Mac OS X 10.10 (14A389)
Report Version: 11
Anonymous UUID: FBE1A538-49FF-2EE1-05A1-7791F7E6BC06
Sleep/Wake UUID: 6A583B00-6011-454B-B7AD-F7341D7CB6CE
Time Awake Since Boot: 51000 seconds
Time Since Wake: 2900 seconds
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Application Specific Information:
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSConcreteTextStorage attribute:atIndex:longestEffectiveRange:inRange:]: Range or index out of bounds'
abort() called
terminating with uncaught exception of type NSException
Application Specific Backtrace 1:
0 CoreFoundation 0x00007fff8df4764c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff97ad06de objc_exception_throw + 43
2 CoreFoundation 0x00007fff8df474fd +[NSException raise:format:] + 205
3 UIFoundation 0x00007fff9850f3f3 -[NSConcreteTextStorage attribute:atIndex:longestEffectiveRange:inRange:] + 133
4 Foundation 0x00007fff8e1e9a68 -[NSAttributedString enumerateAttribute:inRange:options:usingBlock:] + 209
5 Mail 0x00000001003d543a Mail + 1770554
6 Mail 0x000000010027758e Mail + 337294
7 Mail 0x0000000100277186 Mail + 336262
8 Mail 0x000000010027e3fa Mail + 365562
9 Foundation 0x00007fff8e191c73 NSKeyValueNotifyObserver + 382
10 Foundation 0x00007fff8e190e48 NSKeyValueDidChange + 463
11 Foundation 0x00007fff8e1959ad -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 118
12 Mail 0x00000001003601fe Mail + 1290750
13 Mail 0x00000001005046d0 Mail + 3012304
14 Foundation 0x00007fff8e2c52e8 __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 7
15 Foundation 0x00007fff8e1b1905 -[NSBlockOperation main] + 97
16 Foundation 0x00007fff8e19059c -[__NSOperationInternal _start:] + 653
17 Foundation 0x00007fff8e1901a3 __NSOQSchedule_f + 184
18 libdispatch.dylib 0x00007fff95a19c13 _dispatch_client_callout + 8
19 libdispatch.dylib 0x00007fff95a25cbf _dispatch_main_queue_callback_4CF + 861
20 CoreFoundation 0x00007fff8de9ac59 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
21 CoreFoundation 0x00007fff8de572ef __CFRunLoopRun + 2159
22 CoreFoundation