10027 is basically Columbia's zip code. Notably, Lerner Hall falls into this zip code, so all students with a Lerner mailbox have an address of the form: #### Lerner Hall, New York, NY 10027.
In order to ensure proper delivery, however, it is best for students to be more explicit about where their mail is going. Either including "c/o Columbia University," "116th and Broadway," or Lerner Hall's own zip code extension, 7164, seem to work.
South of the campus, many buildings fall into the 10025 zip code.