Verify questionable zip codes and bring an assembled invitation ensemble to your local USPS branch, assessing the proper postage amount needed for your assembled invitation and response set just before sending them out to ensure you don't over-or-underpay for that postage.
Before the post office assesses the postage needed to mail out your invitations, ensure they are not planning a rate increase between the time of postage assessment and mailing them out. The USPS determines postage costs. This is based on regulations including, but not limited to, weight, dimensions, embellishments, envelope shape, and envelope size.
The last thing you want is for wedding invitations to be returned to you for insufficient funds and make the envelope unusable again. Redoing them will cost you more money and time. While at the post office, ask the postal clerk to show you their beautiful wedding stamps.
Ask what's available at your local post office, or browse through a wider variety at the U.S. Postal Service-approved website: www.usps.com or www.stamps.com. Personalized stamps (i.e., photographs, monograms, or logos) are available online. Be sure to verify the validity of using these stamps with your local post office, as some stamp companies are not accepted.
Tips:
If you order a standing invitation, address the envelopes horizontally to save on additional postage.
If you include response cards with your invitations, include stamps on the return envelope to avoid delays.
INTERNATIONAL MAILINGS
For International Invitations, have the post office print a postage label for the exterior envelope. Guests must provide their postage for the RSVP envelope from their respective countries, as the USPS does not sell stamps from other countries.