It's complicated because everyone has their own definition of what Christian means and the historical understanding of the term may not be synonymous with the modern day one, so really it begs the question of which definition do we want to use and how do we justify it? Upon whose authority should be decide upon one? Personally I try to let history speak for itself, which is one of the reasons why out of the various Christianities I chose my Orthodoxy, since I believe it is the most in-line with history and consistent. And that said, the answer is that most of the Church Fathers and Saints whom both the Orthodox and Catholics hold in great revere could not understand Christianity as something apart from the Church. To them being Christian meant belonging to the Church established by Christ on Pentecost and using apostolic succession to distinguish themselves amidst offshoots and heretical groups. The canons of the Church are similar in that they never made any distinction between completely different religions and schools of Christianity apart from the Church. The canons rather recognized them as all the same by virtue of the fact that they were not the Church. And to this day the Orthodox Church maintains the same practice by often requiring that most Protestant and Catholic converts to the Church be re-baptized and renounce their heresies of the past. Both Catholics and Protestants are regarded as non-Christian by the Orthodox Church. But there is a distinction between the two. Protestants are merely dismissed as heathens whereas Catholics are dismissed as schismatics and heretics. The reason for that is because the former never belonged to the Orthodox Church in the first place whereas the latter did belong to it but willingly committed schism in 1054 and violated the canons which, at least by technicality, prescribe anathema to Rome. One big example is Rome's addition of the Filioque to the Nicene Creed. The canons of the 3rd Ecumenical Council as well as the 8th one of 879-80--which Rome not too surprisingly later dismissed as a "robber council" despite having been present at it and affirming it at the time--anathematized anyone who altered the Nicene Creed of anything short of the authority of another Ecumenical Council. Since the insertion of the Filioque did not occur at an Ecumenical Council but a local council in Toledo, Rome is anathema by the canons of the aforementioned Councils. By that same token though, being non-Christian isn't considered as much of an insult in the Orthodox Church as it is for Western Christians. We've never quite understood why they find it so offensive to be called non-Christian and why they use it as an insult, since in Orthodoxy being a non-Christian isn't exactly considered a de facto Hell verdict. Many of the Fathers including Origen of Alexandria, Ss. Basil the Great, Gregory of Nyssa, and Isaac the Syrian held universalist--what they called apokatastasis--leanings which many people within the Orthodox Church still hold today. It essentially rests on the fact that Salvation in the Orthodox Church isn't understood as a mere acquittal verdict but as a lifelong ontological transformation, a healing of sorts called Theosis which only makes sense via the Essence-Energies distinction of the Orthodox Church which Western Christians--particularly Scholastics--reject because it contradicts their doctrine of Divine Simplicity. That said, it takes more than just club membership for Salvation. Just as many people visibly within the Church may not be saved due to their own hardness of hearts or dispositions, the inverse can be said about many people visibly outside of the Church. And so it is possible, although it can never definitively be affirmed, that everyone will be saved. Our modern theologian Metropolitan Kallistos Ware calls this "hopeful universalism." EDIT: Did the group get deleted?

Yes.