You have the option of mailing your letters via USPS First Class or USPS Standard Mail. USPS Standard Mail (takes 7 to 21 business days) is an alternate mail class (only available in the US) that provides lower postage rates, but at slower speeds than USPS First Class (takes 4 to 6 business days and international mailings take an additional 5 to 7 business days). USPS First Class Mail is our default mailing class (available in the US and internationally) that provides higher postage rates at faster speeds.