Why does the "mail" app still show storage after deleting my mail accounts?

[GadgetGuru72]

Hello -

I previously had two email accounts set up in iOS mail -- my personal account, and my work account.

I recently started using Google Inbox for my personal account, and Microsoft Outlook for my work account, so I deleted both accounts from the "mail" app. [Note: I am still syncing the calendar for both, so I simply turned off the "mail" slider for each account].

Now, when I launch the "mail" app, it shows the screen to add a new account, so it appears that the old mail is gone.

However, when I go into settings, then usage, it shows nearly 350MB used in the mail app for "mail and attachments."

How do I clear this out?

Thanks in advance.