Sm1smom
Super Moderator
There are some airports - two I know of, an Irish one and Abu Dhabi - where US immigration procedures are done in the departing airport rather than on arrival in the US. (This is for everyone on flights to the U.S., not just potential immigrants). The "before" is technically correct but all it means is that it happens before you get on the plane rather than after you get off it, so there is no real difference.
And you can throw in Canada on that list too. If flying in from Calgary, AB in Canada for instance, US immigration is completed before boarding the plane in Canada.