How to Delete the User plist in Mail

I've been having trouble with Mail recently (keeps crashing), and I found some tests to do on another topic here. The first thing it said was to create a new user account and test Mail on that - it then said if that worked (which it did), that there would be a problem with the Users plist, and it should be deleted. My question is - is this safe, and if so how do I find the file??

Thanks!