The behavior you're describing (quitting unexpectedly) is what is commonly known as crashing. When an application crashes, the system writes information about the state of the application at the moment of the crash into a log file. That information is called a crash report and it makes troubleshooting much easier because it makes possible to properly identify the exact cause of the crash without having to follow trial-and-error procedures. In order to find and paste the relevant part of the crash report here, do the following:
1. Open
/Applications/Utilities/Console.
2. From the
View menu, choose
Show Log List -- if
Hide Log List is displayed instead, skip this step.
3. On the left pane of the Console window, expand
~/Library/Logs by either double-clicking on it or clicking on the triangle to the left. An item named
CrashReporter appears, expand it as well.
4. Select
Mail.crash.log. The whole Mail crash log appears on the right pane of the Console window. It may contain many crash reports. We only want the latest, which is located at the bottom of the file.
5. Look for a line that begins with "Date/Time:" as close to the bottom as possible, and another that says "Thread N Crashed:", where N is a number. Select everything from the "Date/Time:" line to the lines immediately following "Thread N Crashed:". Copy that text and paste it here.
Do not post the whole crash log, and do not include anything beyond the lines immediately following "Thread N Crashed:" either, just the relevant part. See the following two threads for examples of what a crash report looks like (the "Binary Images Description:" part in the second example is useless to me, so I'd prefer you to not include it):
http://discussions.apple.com/thread.jspa?threadID=439295
http://discussions.apple.com/thread.jspa?threadID=441465
