To what extent is Harav Moshe Feinstein`s pesak of Cholov Akum applicable today in contemporary times and circumstances? Many thanks for you fantastic service!
The heter is relevant today as it always was. Meaning, Rav Moshe clarifies that according to the strict halachah non-supervised milk is kosher in countries where government regulations ensure that it is cow milk alone, and this halachah remains true today.
However, Rav Moshe himself encourages the consumption of supervised milk in a number of places, and this encouragement can be adhered to far more easily today than in bygone times, so that it can be said that in practice, today it is proper to be more meticulous in the matter than it was in previous generations. Still, when one encounters extraneous circumstances, it remains just as permitted today to rely on Rav Moshe’s heter as it always was.
The heter, of course, does not in fact originate with Rav Moshe, and it draws from the ruling given by the Peri Chadash that the prohibition of Chalav Akum is not a full enactment, and therefore if we know that the milk is kosher, it is kosher on a rabbinic level too. The Chasam Sofer disputed this position, and based on his ruling many are stringent, but those who rely on Rav Moshe have upon whom to rely.