Mail is categorized by size, shape, service selected and destination. For letters, the options narrow to service selected and destination. The U.S. Postal Service provides a number of mailing options for simple letters, and the cost will depend on where it is going and how fast you want to get it there.

International Mail

The maximum size for international letters is 6-1/8-inches by 11-1/2-inches. The USPS provides a list of countries and localities where mail may be sent with cost information and any limitations regarding letter content. Send international mail by Global Express Guaranteed, Express Mail, Priority Mail or First-Class Mail. Extra services include registered mail, insurance, restricted delivery and return receipt.

Express Mail

Express Mail delivers letters seven days a week and 365 days a year. It is the fastest and most expensive way to mail a letter, but delivery is guaranteed overnight. You can track Express Mail online and request a signature upon receipt without additional charge. Use flat-rate envelopes or purchase postage separately, even online.

Priority Mail

Stock up on Priority Mail flat-rate envelopes and supplies by ordering online or picking them up at the post office. Delivery time on Priority Mail is one to three days with pricing based on flat rates or zoning. Choose Priority Mail for quick, reliable delivery of less-urgent letters and track it online. Unlike Express Mail, Priority Mail is not delivered on Sundays and the timing of delivery is not guaranteed.

First-Class Mail

Buy a book of stamps to send letters under 3.5-ounces via First Class mail. Cheaper than both Express and Priority Mail, First-Class mail typically delivers within one to three days. The speed will depend on the distance it travels. First-Class mail is the most common delivery method for business correspondence, bills and personal letters.