c# - any examples of adding filter criteria for a User List call?

Probably a stupid question on my part but have to ask. How do you add filter criteria to a User List call in the REST API? Using C#, I am trying to lookup a user based on email address. I have tried a few approaches like: var values = new NameValueCollection(); values["EmailAddress"] = email; values["PageSize"] = "5"; values["IncludeHidden"] = "false"; var xml = Encoding.UTF8.GetString(webClient.UploadValues(requestUrl, values)); and var data = "" + email + "5false"; var response = webClient.UploadData(requestUrl, "POST", Encoding.ASCII.GetBytes(data)); var xml = ASCIIEncoding.ASCII.GetString(response); to no avail. Both methods simply return the first batch of all records. Thanks in advance.