As in sent messages in the private messages from the forum? If so click each box to the right or click where is says total messages 7 or however many u have....and at the bottom where it says "selected messages" click drop down and select delete then hit go
If you meant using the iPad's native Mail app, then the answer is 'yes' and 'no'.
If you're in the Mail folder that you to delete messages from (i.e. 'Sent'), press the 'Edit' button that appears towards the top of the screen. Now each message in the 'Sent' folder has a small 'radio button' next to it. Briefly touch each of the messages that you want to delete and the radio button gets a 'tick' or 'check' mark in it. When you've marked all the messages you want to delete, simply press the 'Delete' button that's near the bottom of the screen. That was the 'Yes' answer....
The 'No' answer is that there's no 'Select All' option that allows you, in one move, to select, say, all the messages in the 'Sent' folder and then delete them all at once.