The Sort command is in the Utilities & Settings menu.
Use the Sort command to sort the current list. You can sort by any item in an address simply by selecting it with the mouse: First name, Last name, City, State, Zip, etc.
Note: FastEnvelope will notify you if it had a hard time finding the proper field to sort on. You should check your list after this message. There is no way to drag items in the list into position: all sorting must be done with the Sort command.