One email crashing mail app

Hey guys, i have this one email and for some reason has so many reply threads it is 555KB. Itll open this email fine, if I try to reply itll let me type it.. and then when I hit send it will go back to the original email and sit there.. the little circle loader icon on the top freezes and eventually the iphone restarts. The reply never makes it out of the iphone. I figure this since when it restarts its not in the sent. Anyone else experience this?