I found it now, didn't know there were two libraries.
So I did as you said, but the mail does still not open.
I now get these messages:
06.11.14 22.44.40,881 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
06.11.14 22.44.41,217 Mail[2861]: Using V1 Layout
06.11.14 22.45.22,727 com.apple.iCloudHelper[2864]: objc[2864]: Class FALogging is implemented in both /System/Library/PrivateFrameworks/FamilyCircle.framework/Versions/A/FamilyCircl e and /System/Library/PrivateFrameworks/FamilyNotification.framework/Versions/A/Famil yNotification. One of the two will be used. Which one is undefined.
06.11.14 22.45.22,778 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
06.11.14 22.46.50,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.46.59,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.46.59,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.46.59,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.46.59,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.46.59,000 kernel[0]: Sandbox: storeuid(525) deny mach-lookup com.apple.dock.server
06.11.14 22.47.01,436 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
06.11.14 22.47.01,784 CoreServicesUIAgent[1969]: unexpected message <OS_xpc_error: <error: 0x7fff7a576c60> { count = 1, contents =
"XPCErrorDescription" => <string: 0x7fff7a576f70> { length = 18, contents = "Connection invalid" }
}>
06.11.14 22.47.03,108 Mail[2868]: Using V1 Layout
06.11.14 22.47.03,452 Mail[2868]: Upgrading Library from 4.188 to 4.188
06.11.14 22.47.09,075 Mail[2868]: unresolvedBaseMailDirectory /Users/helg/Library/Containers/com.apple.mail/Data/Library/Mail
06.11.14 22.47.09,075 Mail[2868]: resolvedBaseMailDirectory /Users/helg/Library/Mail
06.11.14 22.47.09,888 mds[38]: (DiskStore.Normal:2376) c8001 1.000009
06.11.14 22.47.10,430 mds[38]: (DiskStore.Normal:2376) a001 1.000004
06.11.14 22.47.17,092 Mail[2868]: Capturing diagnostics to trace took 8.015999
06.11.14 22.47.52,223 Mail[2868]: Exception during migration: data parameter is nil
06.11.14 22.47.52,224 Mail[2868]: Migration (simple) failed and took 43.149814 seconds
06.11.14 22.47.53,623 Mail[2868]: emlxCountPreMigration 12360
06.11.14 22.47.53,624 Mail[2868]: emlxCountPostMigration 12395
06.11.14 22.47.53,624 Mail[2868]: lostAndFoundEmlxCount 0
06.11.14 22.47.53,624 Mail[2868]: messageCountPreMigration 7166
06.11.14 22.47.53,625 Mail[2868]: messageCountPostMigration 7166
06.11.14 22.47.53,625 Mail[2868]: MessageTracing took 1.398823
06.11.14 22.47.53,625 Mail[2868]: Upgrade failed because of exception: data parameter is nil
06.11.14 22.47.53,626 Mail[2868]: Library upgrader failed: Error Domain=MCMailErrorDomain Code=1029 "data parameter is nil" UserInfo=0x7ff72c889920 {NSLocalizedDescription=data parameter is nil}