The Talmud says milk is not kosher unless a Jew supervises the milking, to be sure it's just kosher-animal milk. Assuming one goes by the ruling of R' Moshe Feinstein and others that "knowing" is ...
Regarding the rabbinic decrees instructed in the Talmud, how can one know that a particular rabbinic commandment is binding to all future generations and may not be rescinded or amended ever? . ...