Here is a red envelope we received form MercyCorps. The letter inside was a mail merged laser letter 8.5 x 14 with a detachable form that was perforated.  Inside was a #9 reply envelope with a giant window envelope.

The thing that we liked about this mailer was the red airmail style envelope. It gets attention and generates a sense of urgency. Nice job MercyCorps! good luck with your campaign.

Mercy Corps direct mail envelope