I have removed all mail accounts from my iPhone and reset it. What's using storage?

I have deleted all my e-mail accounts from Mail from the iPhone -- iCloud, my work account, etc., and have reset the phone (powering off and then back on) a couple of times. In Settings/General/Storage, I still show 186 MB of data being used by mail. Is the Mail app itself 186 MB? If not, how can I free up some of the space being "used" when there are no accounts at all on the phone?