In every version of OS X that I can remember until Sierra, there was an option in Mail to remove sent messages after a week, month, and maybe even a year. A couple days ago I noticed that my sent mail folders were filled with messages from a couple months ago. I looked in the Mail preferences and saw that the option to delete sent messages after a certain period of time has been removed. Is there a way to get this back, perhaps through some plist wizardry? This is highly annoying.