To be eligible for the normal letter rate, an envelope must be at least 6.125 inches tall by 11.5 inches long and have a thickness of at least 0.25 inches. Anything larger than these dimensions will require extra shipping. If you aren't sure if your envelope meets these requirements, call our customer service team at 1-800-462-6775. There are three types of letters that can affect their rate: urgent/first class, standard, and express. Urgent/first class letters are sent through the United States Postal Service (USPS) priority mail system and require a $15 fee per letter. Standard letters go through the regular first-class mail system and cost $5 to send. Express letters use a special delivery service and are delivered within one business day for $20. There is no charge for this service. The amount charged for postage increases as weight increases. For example, a letter under 5 pounds costs $0.45 first class, $1.50 standard, and $9.00 express. A postcard runs $0.35 first class, $1.10 standard, and $6.00 express. In addition to determining how much it will cost to send your letter, you will also need to know its final destination to find out whether it needs extra postage.