According to Pitman’s Commercial Typewriting, 9th Edition 1965:
“An address of three lines should be double spaced. Single or double spacing may be used for an address of four lines; for more than four lines use single spacing, except in cases where very large envelopes are used, where double spacing or even treble spacing may be preferred.
That’s the theory. Here’s the reality …
Failure isn’t an option, it’s a style choice.
Actually that last one’s purrrfect!