Question: "Someone has been insisting to me that the Russian Orthodox Church recognizes the validity of the Sacraments of the Roman Church. And in fact, have since at least 1776. Metropolitan Hilarion Alfeyev said something to this effect as well at one point, but I'm not sure I buy it, how would you respond?"
I think they probably meant to say "since at least 1666-1667, which were the dates of the a controversial council in Moscow, which condemned the Old Rite, and deposed Patriarch Nikon. That council is a topic unto itself, but the documents of that council do speak of "valid" Roman Catholic sacraments. But one can find this expression in one of the oldest Liturgical texts published in English, which is still widely used today -- the Hapgood Service Book, translated by Isabel Hapgood, with the blessing of St. Tikhon of Moscow.
Even in the Ecumenical Canons, we find provision for receiving converts from certain groups by means other than baptism, though included among those canons is the canon of St. Cyprian of Carthage that states that there is no true baptism outside of the Church. This canon was affirmed by the Sixth Ecumenical Council in its second canon. However, that same canon also affirmed the canons of St. Basil, and his first canon, provides a bit more nuance. He agreed that the Church is under no obligation to recognize baptisms that take place outside of the Church, but states that for the sake of "economia" the Church may do so, though he also noted that in different regions, different practices prevailed when it came to how certain heretics or schismatics were received. So in terms of theological principle, we affirm that there are no sacraments, in the fullest sense, outside of the Church, but the Church does receive converts from heterodox or schismatic groups by economia -- which could mean that we chrismate them, or in some cases that we simply accept them by confession and a profession of faith. And in the Hapgood Service, there is a service provided for this very purpose.
Beginning on page 454 of the Hapgood Service Book, there is a service entitled "THE OFFICE FOR RECEIVING INTO THE ORTHODOX FAITH SUCH PERSONS AS HAVE NOT PREVIOUSLY BEEN ORTHODOX, BUT HAVE BEEN REARED FROM INFANCY OUTSIDE THE ORTHODOX CHURCH, YET HAVE RECEIVED VALID BAPTISM, IN THE NAME OF THE FATHER, AND OF THE SON, AND OF THE HOLY SPIRIT".
But the question we have to ask is, what does it mean when it speaks of "valid baptism"? First off we should ask, what does true baptism do? Among other things, it unites one to the Church. But right after the above quoted heading, it says: "The power of granting absolution to such persons, and of uniting them to the Church properly devolveth on a Bishop. Nevertheless, that the converts to Orthodoxy may not be tempted to return to their heresy by reason of delay, it is wiser and more expedient that the Bishop should delegate his power, and grant his blessing therewith, to a Priest well versed in divine lore, and who is competent to instruct such a person in the articles of the Orthodox faith, and to correct his erroneous opinions." And so if a "valid baptism" outside of the Orthodox Church united one with the Church, there would not be a further need for any service to unite them to the Church, but that is precisely what this services is intended to do.
The first question the convert is asked is "Wilt thou renounce the errors and false doctrines of the Roman-Latin [or Armenian, or Lutheran, or Reformed) Confession?" and then they are asked "Dost thou desire to enter into and abide in the communion of the Orthodox-Catholic Faith?" And after the convert is asked to renounce specifically the false teachings of their former confession, and to affirm the basic tenets of the Orthodox Faith, they are told "Enter thou into the Orthodox Church; and cast away all the errors and false doctrines wherein thou hast dwelt: and honor the Lord God, the Father Almighty, and his only-begotten Son Jesus Christ, and the Holy Spirit, one true and living God, the holy Trinity, one in essence and indivisible." And all of this is in the service that would be used, even for those being received by confession and profession of faith. This service makes it abundantly clear that we are uniting someone to the Church who was previously not united to the Church.
So what happens when the Church accepts a baptism that was done outside of the Church, by economia? St. Augustine compared baptism to the "military mark" which was a tattoo a soldier was given when entered the Roman Army, and it showed what commander he belonged to. St. Augustine said that such a mark could be retained by deserters (schismatics), and it could illicitly be given to those who had never been in the army, and yet unless and until such men actually joined (or rejoined) the army, those marks did not have the real significance that they should have... however if they did rejoin or join the army, the mark would not need to be redone. And so what happens when someone is received by economia is they are finally united to the Church, and their baptism is then given the real meaning of what true baptism is.
And so when we speak of "valid" Roman Catholic Sacraments, we mean that they are valid in the sense of their outward form. I have not seen any official Russian Orthodox statements that said that the Roman Catholic eucharist was "valid", and this is because we can receive a convert who was been baptized by economia, and we can even receive a Roman Catholic Priest in rank, by economia... but we could never receive the Roman Catholic eucharist by economia. This does not mean that we say that Roman Catholics are all going to hell, or that their worship and devotion to God has no meaning to God. Those things are between them and God. This is not a matter for us to pass judgment. We also pass no judgment on the souls of those outside of the Church, but we can say that at least in this life, they remain outside of the Church until and unless they are received into the Orthodox Church.