The "correspondence" referred to in the encyclopaedia is that of her Letters. Since she was of such great fame, many texts were attributed to her to give them greater station, in addition to her authentic writings. That's what the encyclopaedia is warning readers about in the paragraph that you quoted in the above post, to beware spurious texts circulated under her name. All of the letters that modern scholarly works rely upon are her authentic ones, not the spurious. Unfortunately, a lot of spurious works float around on the net under her name that were not by her. I've been rebutting them repeatedly and directing interested readers to the authentic writings. St. Hildegard believed that all of her visions were revealed to her directly by God. Her authority as a Doctor of the Church rests in her epic visionary theology. In Scivias, she wrote about the mode by which many of these "visionary experiences" were transmitted to her: https://books.google.co.uk/books?id=8zJOQ52E4GMC&pg=PA106&dq=The+visions+I+saw+I+did+not+perceive+in+dreams,+or+sleep,+or+delirium,+or+by+the+eyes+of+the+body,+or+by+the+ears+of+the+outer+self&hl=en&sa=X&ved=0ahUKEwie3-f50q7VAhUoKsAKHURTBv8Q6AEIJzAC#v=onepage&q=The visions I saw I did not perceive in dreams, or sleep, or delirium, or by the eyes of the body, or by the ears of the outer self&f=false When I was forty-two years and seven months old, Heaven was opened and a fiery light of exceeding brilliance came and permeated my whole brain, and inflamed my whole heart and my whole breast, not like a burning but like a warming flame, as the sun warms anything its rays touch. And immediately, I knew the meaning of the exposition of the scriptures... But I had sensed in myself wonderfully the power and mystery of secret and admirable visions from my childhood - that is from the age of five years - up to that time, as I do now... The visions I saw I did not perceive in dreams, or sleep, or delirium, or by the eyes of the body, or by the ears of the outer self, or in hidden places; but I received them while awake and seeing with a pure mind and the eyes and the ears of the inner self, in open places, as God willed it. How this might be is hard for mortal flesh to understand. St. Hildegard differentiates between the "inner" and "outer" senses, as many other medieval Catholic theologians did before and after her. She claimed to receive her visions via the mind's eyes and ears: auribus interioris hominis, mediated not through dreams or hallucinations but in a waking vision interiorly, in a manner beyond the comprehension of the physical senses. This is what St. Paul referred to in 1 Corinthians 2:9 - What no eye has seen, what no ear has heard, and what no human mind has conceived -- the things God has prepared for those who love him This is the same manner in which the Beatific Vision of the Divine Essence will be enjoyed by the blessed in heaven, as another Doctor of the Church St. Thomas Aquinas explained in his Summa Contra Gentiles: "...If God's essence is to be seen, the intelligence must see it in the divine essence itself, so that in such vision the divine essence shall be at once the object which is seen and that whereby it is seen. This is the immediate vision of God that is promised us in Scripture: 'We see now in a glass darkly, but then face to face' (i Cor. xiii, 2): a text absurd to take in a corporeal sense, as though we could imagine a bodily face in Deity itself, whereas it has been shown that God is incorporeal...Nor again is it possible for us with our bodily face to see God, since the bodily sense of sight, implanted in our face, can be only of bodily things. Thus then shalt we see God face to face, in that we shall have an immediate vision of Him, as of a man whom we see face to face. By this vision we are singularly assimilated to God, and are partakers in His happiness: for this is His happiness, that He essentially understands His own substance. Hence it is said: 'When He shall appear, we shall be like Him, for we shall see Him as He is' (i John iii, 2). And the Lord said: 'I prepare for you as my Father hath prepared for me a kingdom, that ye may eat and drink at my table in my kingdom' (Luke xxii, 29). This cannot be understood of bodily meat and drink, but of that food which is taken at the table of Wisdom, whereof it is said by Wisdom: Eat ye my bread and drink the wine that I have mingled for you (Prov. ix, 5). They therefore eat and drink at the table of God, who enjoy the same happiness wherewith God is happy, seeing Him in the way which He sees Himself..." - Saint Thomas Aquinas (1225–1274), Summa Contra Gentiles St. Hildegard considered herself to be God's mouthpiece.