In the future. Pressman, like many patent practitioners, has embraced the electronic filing system (EFS-Web) He recommends that in the future you consider filing electronically, because that way you get an instant filing receipt and serial number. (And if you're a registered efiler you can also instantly view the application details on the USPTO's Private PAIR site.)
Speaking of patents and mailing ... Isn't this 1969 patent (above) for mailing vinyl singles the cutest thing?