When a message needs to be delivered with lightning speed, you can count on First-Class Mail (FC mail). One of the more well-known direct mail terms on this list, FC mail simply refers to mail sent quickly. This may be a postcard, large envelope, letter, or small package—anything less than 13 ounces. If more than 13 ounces, it becomes priority mail. When using Lob, businesses can expect first-class mail to be delivered in 4-6 business days from an API request. By comparison, standard mail takes about 7-21 business days.