Yeah, it sux having to select emails one at a time to send to the trash BUT once they all in the trash, u can select delete all and it will do so.
Also, I just thought of something else that might help/ be easier n faster. Let's say for example all these emails u speak of is thru aol. Well just go to aol website thru safari or 3rd party browser app. Pull up the mail on the browser. U gonna have to sign in to whatever email service on the browser u choose. Like for aol, all ur mail will pop up in the mailbox like when u do it on a desktop. There are boxes by all ur emails then there is a box at the very top. U click the empty box at the very top, and it will check off all of ur emails. Then select the delete button. Then it will ask u do u want to delete all selected. Press yes. Then it will delete. If u have that many emails, u probably gonna have multiple pages of emails. Just repeat process for each page of emails u have as this is wayyyy faster thn one at a time. Once done deleting, go to ur email trashcan, and empty it. This will permanently empty ur mailbox of emails u deleted.