If you're trying to delete a bunch of emails/texts (I'm gussing that's what "en masse" means), this can be done in a few ways.
1)open the folder > highlight a group of messages > delete
2) if you want to erase all messages from before a certain date: highlight the date > BB button > Delete Prior
Thanks - RickyRoss10, my problem is I don't know how to highlight a bunch of them at the same time.
Using two fingers (there may be a better way, but this is what I use) hold one finger on the email you want to start the group with and use the other to select to bottom-most email.