The Door of Night

[Elrian]

But Morgoth himself the Valar thrust through the Door of Night beyond the Walls of the World, into the Timeless Void; and a guard is set forever on those walls, and Earendil keeps watch upon the ramparts of the sky.

It says and a guard is set forever on those walls, AND Earendil keeps watch upon the ramparts. The only ones who could keep watch are Vala or Maia, The Elves cannot go there. Earendil never leaves his ship, nor does he stay in one place to gaurd, he sails the sky. The Door of Night is not on the ground but set in the Walls of the World between Ea and the Void. The Valar would know of Sauron's approach and be there to greet him. Yes Sauron is a liar, he lied as Annatar about the rings and himself.