To select all the messages in your box, click the check mark box that's in the header section of your emails (Where it says sender, subject, date, size, etc) then you can click delete.
same question but in the inbox now (it used to be possible with one click in the box) you can only do it 30 at a time. verizon just sent me an e-mail asking me to trim that down but there are 150 times 30 messages in there. gotta be an easier way than 30 at a time. any ideas? thanks.