Special Agent Scott Balfour says it took three mail trucks to remove the letters from the home of an unidentified letter carrier who worked in the city's Bustleton neighborhood.
Balfour says some of the mail dates back to 1997.
Postal officials say they recovered the mail on April 28 and it was being delivered to customers this week.
Balfour wouldn't comment on what prompted the investigation but said the postal carrier hadn't been to work since February.
Balfour says postal officials are still trying to find the man so they can question him.
While the Postal Service had not released the carrier's name, Action News has learned his name is David Blauser from the Port Richmond section of Philadelphia.
