Mail delivery time varies depending on the mail carrier, the type of mailing service and the source and arrival destinations of the mail. U.S. Postal Service asserts that delivery of domestic First-Class Mail, the most used mailing service for letters and small packages, takes about one to three business days.
Aside from First-Class mail, other U.S. Postal Service delivery options include Priority Mail, Priority Mail Express, Standard Post and Media Mail. According to USPS.com, Priority Mail shipping times are estimated between one to three business days, while Priority Mail Express is guaranteed overnight. Standard Post and Media Mail are both estimated at two to eight business days. For international mail, U.S. Postal Service delivery times vary greatly depending on the country, ranging from several days to several weeks.