[Legate of Amon Lanc]

Originally Posted by Gordis

I don't think it could be taken literally. Saruman knew who Gandalf was and would have told Sauron, if the other didn't know about the Istari already.

Nay, why would he do that? Sauron might have guessed it, or forced it out of him, possibly, but Saruman had no need to tell him from his own initiative. Saruman was very clever and aware of the fact that having more knowledge than those around him is always advantageous for him.

I think Sauron came to know about the Istari and Gandalf in particular much-much earlier - for hadn't he run away when Gandalf came to Dol Guldur the first time in 2063? Sauron had been so afraid of him that he hid for 400 years somewhere in the East.

That's possible. But it's also possible that Sauron simply was not strong enough yet back then and even though not knowing who he is, he felt him powerful (something like if Elrond came there) and so he decided to escape. Gandalf had already quite some time of his actions in M-E, so Sauron might have learned about him being a powerful figure, and he did not necessarily have to know who he was.

Also consider that the Witch-King knew about Gandalf, (maybe from Sauron, maybe from personal experience during his rule of Angmar), recognized his power and feared his involvement with the Ring:

Well, this does not necessarily say he knew what Gandalf is. He might have known he is a dangerous enemy, well indeed, he was, that much was clear to Sauron, surely - like Saruman, or Elrond, or Galadriel, or whoever else. And if Gandalf indeed was in Dol Guldur and escaped from there, then Sauron knew he has a really powerful enemy in him. And yet he did not need to know his true identity.

As for the Mouth, he did as instructed, showing contempt to both Gandalf and Aragorn - however he was much afraid himself.

His fear was caused by the "kingly charisma" of Aragorn.