Only the ones from the postmaster upon leveling up Cryptarch
Since the patch there is zero chance of a legendary engram producing a rare item.
If I read your message right, you're misinterpreting what that package is. I find a lot of people don't understand that package for some reason.
The package itself is purple in color. It's a box, nothing more. The color of the package does not indicate what's inside of it, the tooltip for the package says what could be inside of it.
The Cryptarch leveling reward package pretty clearly states that it can contain rare items and lengendary items. The engrams that pop out of that package will produce the reward and if a legendary engram pops out, it will produce a legendary reward, every time, guaranteed.