Two possible remedies, and I'd try in this order.
1) Safe Boot, then reboot normally (Read about Safe boot mode in the Help menu)
2) Reset PRAM. This a software reset that I just tried yesterday to fix nuisance problems in 2 Macs that did not respond to a Safe boot.
Crashes like you describe often indicate there is a software screw-up somewhere in the OS. How it got out of whack is going to be tricky to solve, Unless you are good at understanding Console messages. You could try typing Crash in the Console filter blank to see what might snow up.
The 2 steps above are what I would use to attempt a repair.
The next 2 steps are more time consuming, but may be required:
A) Download and re-install the Combo update for your OS.
B) Reinstall the OS, then the Combo update.
Your settings and data are safe in both cases UNLESS you "erase and install". That would require complete backup beforehand to save important data/files.
Go to ~/Library/Containers/com.apple.mail/Data/Library/Preferences and move the file com.apple.mail.plist to the Desktop and restart Mail.
Other plist files exist in ~/Library/Mail/V2/MailData/ but I'd start with the above plist first. In this directory you could also manually remove the offending account (particularly if the mail is also stored online) and re-add it.
Best Answer
You can reset Mail's settings by running the following one-liner in Terminal:
https://georgegarside.com/o/se/reset-osx-mail.html