When sending an envelope through the U.S. Postal Service, you must place sufficient postage on the envelope. If you do not affix enough postage, the post office generally will return the envelope to you; in rare cases, the item will be delivered "postage due". This means that the addressee may have to pay the shortfall. If one stamp isn't enough to cover the postage, use more. This is acceptable, as long as the return address and mailing address are easily visible by the postal employees.
Determine the weight of the envelope and the postage necessary. If you have a postage scale, weigh the envelope. Visit the U.S. Postal Service website for a chart detailing postage rates for envelopes. If you do not have a postage scale, visit the post office and have your envelope weighed there.
Determine the proper postage for your envelope. Envelopes for regular letters generally are mailed First Class, and can weigh no more than 3.5 ounces. In 2019, the First Class rates were increased to 55 cents for letters weighing up to one ounce. Each additional ounce or fraction of an ounce, costs 15 cents. For example, a 2-ounce letter costs 70 cents to mail First Class. a 3.5-ounce letter costs $1.00.
A standard First Class or Forever stamp costs 55 cents; in addition, the Postal Services sells stamps in several other denominations, including a 2-ounce stamp for 70 cents, a 3-ounce stamp for 85 cents and a postcard stamp for 35 cents.
Place the postage stamps on the upper right corner of the envelope. When more than one stamp is required, begin placing the stamps in the uppermost right corner and place additional stamps in a line across the top of the envelope right next to each other. Stop placing stamps when you are about 2 inches away from the return address (in the upper left corner). Continue placing additional stamps in another row underneath the first row, if necessary.
Stamp placement is important, and the postal service will return your letter or postcard if the stamp (or stamps) are placed anywhere but the upper right hand corner of the envelope or postcard. If you accidentally put a stamp on the left side, peel it gently from the envelope and place it correctly. You may have to cut the stamp from the envelope if it does not peel away easily. In this case, you'll have to address a new envelope. Affix the stamp correctly using a small amount of glue suitable for paper.
Do not place stamps so that they obstruct or obscure the return address or the mailing address. Instead, purchase a postage meter strip for the exact amount directly from the post office, place it on your envelope and mail it.
Hang on to older unused stamps of varying denominations. Postage never expires, though once cancelled, it cannot be reused. You can always use older stamps to meet modern postage requirements.