How to Correctly Write an Address on an Envelope: Complete Step-by-Step Postal Guide
Affix your postage stamp firmly in the upper-right corner. Keep roughly 1/4 inch of clear margin from the top and right edges. Never let the stamp overlap the recipient's address lines, and avoid placing stamps on the back flap.
A standard First-Class Mail Forever stamp covers a standard rectangular envelope weighing up to 1 ounce. If your letter exceeds one ounce, contains thick rigid cardboard, or uses square or irregular envelope dimensions, you must add supplemental postage or a non-machinable surcharge stamp. Square envelopes cannot pass through mechanical sorting belts without jamming; postal carriers must process them manually. Applying insufficient postage will either result in the letter bouncing back to your return address or arriving at the recipient's doorstep with a "Postage Due" fee notice attached.