Yn.zip -

In many digital document scans, "YN" followed by "ZIP" is simply a placeholder for "City, State, Zip " or a Yes/No field near a zip code entry.

Because "YN" is a common two-letter abbreviation, the term "yn.zip" occasionally appears in modern contexts as a coincidence of formatting rather than the historical software:

It was designed for CP/M , an operating system that preceded MS-DOS and was widely used on microcomputers in the late 70s and early 80s.