Assuming the newsletter is in HTML format? Two suggestions that work for me:
1. Send the subscriber to a web page with the coupon that can be printed or a link to a PDF document that the subscriber can save or print.
My best results are to send the subscriber to a web page where you can also create more offers, adverts, etc. The objective is to push the subscribers out of the email box and into your market fold.
Tip. Publish your newsletter online (Newsletter Archives) so that people "not" on the list also have access to your offers, adverts, etc. Some newsletter publishers also create a new link to the online newsletters using TinyURL when you have a subscribers special "only for subscribers." Explain that to them and they feel privileged.
2. Last, but not least, instruct the subscriber to print the email.
Jeffery 100% :-)