It appears many people don't know about this. I had to have it pointed out to me by my loving wife.
Step 1. quickly read your mail. don't take attachments or delete messages.
Step 2. return to inbox. There is a menu drop-down on the LEFT side of the mailbox.
Step 3. from this drop-down, choose "accept all attachments". Boom. done.
Step 4. from the same drop-down, choose "delete all read messages". Boom done.