You can also use the select all, and then the 'take all' button. Just two clicks, and you have both attached cash and items back. But make sure you don't accidentally hit the 'delete' button in between, since it has NO confirmation (yes, I found out the hard way, with several mails with attachments selected, ouch!)
I did that with my commando. Fortunately it was all read e-mail with no cash/attachments. Those little "thank you" type e-mails you get from NPCs that vanish after 30 days.