iPad Recovering Space

I created a temporary email (IMAP) account to test it out, sent some test emails (with images) and then deleted the account. The problem is, the sent emails are now taking up space and even if I "recreate" the account, the ipad considers it a new email acct and I cannot get to the "sent" emails from the old account to delete them.

So, how do I delete them? I tried Settings -> General -> Manage Storage, but that is information only.