The RSVP envelope is used by your guest to mail back their completed RSVP card. It should have your mailing address on the front and be affixed with the correct postage amount. The RSVP envelope along with the RSVP card must be smaller in size than your wedding invitation so that all these items fit in the outer envelope to mail out to your guests.Zazzle, the printer, provides blank white envelopes with your order of RSVP flat cards. If you want Zazzle to print your mailing address on the front of the RSVP envelopes, you will have to purchase these separately. The printed envelopes will also take longer to ship than your flat cards. So please give yourself additional time to receive them. If a matching printed envelope is available for your chosen design, we showcase it in our matching products section.Don't forget to check out the fabulous customizable matching postage stamps you can purchase to pre-pay the postage for your RSVP envelopes.