[Zigûr]

The quotes we've examined here from the letters and so on, however, imply if not outright state that Sauron knew or at least accurately guessed that the Wizards had come from Aman, although he believed that they had been sent to exert Manwë's will over Middle-earth and not, as was actually the case, to assist Men and Elves in resisting him. He must surely have assumed they were Maiar; what else could they have conceivably been?

That being said, he must have observed that the Wizards were Maiar of a significantly lower stature than himself - he was one of the great among the Maiar, perhaps of comparable stature to, say, Melian, Eönwë, Ilmarë, Ossë and Uinen - albeit perhaps not quite as mighty as these particular examples, and certainly not by the end of the Third Age. In a footnote to letter 183 Professor Tolkien observes that Sauron was an angelic spirit "Of the same kind as Gandalf and Saruman, but of a far higher order." Were some Maiar scarcely more powerful than Elf-lords? Perhaps even, in some respects, weaker? This might explain why Sauron was not threatened by their presence if he understood their nature (if not their intentions or purpose).

I don't believe Sauron would have hunted the Ring personally in any event. He did almost nothing personally in the Third Age.