The user has contributed quite a lot to this site, see here.
What should we do with his posts?
In general, we recommend evaluating each post based on its content, not based on whatever the reader knows or assumes about the identity of the author.
I would suggest that this case is generally no different. If there are high-quality posts associated with this user, they should be treated as high-quality. Low-quality posts should be treated as low-quality.
If any posts violate our anti-spam rules requiring that users disclose their affiliation if their posts promote a product that they're associated with, those posts should be flagged and dealt with as such.
I don't think we should do anything. As far as I can tell, the user has not violated any site rules by posting, or by giving the impression of being a rabbi. Anyone is allowed to post here as long as they follow the rules, even if they are not a rabbi, or even if they are not Jewish.
Moreover, it is not our job to police content based on the identity or worldview of users. Any content that is posted is subject to the same system of peer review as anyone else's content. I see it as a dangerous slippery slope to police content in this manner. It is not such a big leap from deleting content because it was posted by a Christian missionary to deleting content because it was posted by someone from a different branch of Judaism, or someone with a "wrong hashkafa" or from a "bad yeshiva". And it would only be downhill from there.
I do not think we should provide this fellow a further platform for his deliberate deception: his profile picture (which currently looks like a religious Jew, complete with tefillin) should be removed, his username ("Rabbi Michael Tzadok") changed to "spreading the good news of Jesus" or some such, and his "about me" removed also — or changed to something honest.
If you want to leave his answers and questions on because it is the job of the reader to look up the sources and not rely on the post itself ,I can hear. However , to leave his info about himself proclaiming to be a Rabbi and religious Jew is out right irresponsible. If anything his info should have an additional clause stating that upon recent news this person has been found to be a fraud and a link to the many articles provided.