Messages from "No Sender"

It sounds like someone's computer has a virus of some sort that is using the email program to send junk to everyone on the address list. Best thing is to delete.

Hold the iPad in the horizontal position, so the sidebar stays active, tap edit, then tap each email on the left side (little circle), keep doing through them and then tap Delete.

Go to Mailboxes, Trash and tap edit, then Delete All at the bottom of the sidebar, and confirm Delete.

If these things keep coming, you might have to go to Settings > Mail and delete the account, or at least delete the incoming so it can't see the iPad.

That is strange that a little circle does not show on the left side of each email...that should be a default of Mail. It isn't there until you tap Edit in the top right of the sidebar top bar...have you done that and the circles still do not appear?

If you swipe the individual messages does the delete button come up?

Sorry, when you're in landscape mode the the message list on the left, swipe the message in the left column and see if the delete button comes up.