The authenticity of the correspondence has been challenged, on the grounds that it has little in common with the otherwise attested chronology, language, borders and economy of the Khazars at the time.
[1] The alleged correspondence originated with Hasdai ibn Shaprut, foreign secretary to Abd ar-Rahman III, the Umayyad Caliph of Cordoba and al-Andalus.
A man of extensive contacts and virtually unlimited resources, Hasdai is said to have learned of the existence of the Khazars from Khorasani merchants.
His ignorance of the Khazar state is odd, and may even have been disingenuous, either on the part of a potential forger, or Joseph's statements to the effect that there had been communications between the two communities in the past.
Eventually Hasdai's letter is said to have been given to Jews attached to a Croat embassy, and reached Khazaria via yet another messenger, Isaac ben Eliezer of Nemetz (Germany).
Joseph's alleged reply gives an account of Khazar history and of its current (c. 960) sociopolitical and economic status.
Historian Peter Benjamin Golden wrote that "Dunlop and most recently Golb have demonstrated that Hasdai's letter, Joseph's response (dating perhaps from the 950s) and the 'Cambridge Document' are, indeed, authentic.
"[2] Historian Shaul Stampfer has questioned the authenticity of the letter said to have been received from the Khazar king, citing numerous linguistic and geographic oddities amid a flourishing of pseudo-historiographic texts and forgeries in medieval Spain.
[3] Authenticity of the conversion story in the letter was dismissed by the early 12th century Talmudic scholar Rabbi Judah of Barcelona.
You made us happy and we are delighted with your understanding and wisdom.... Let us, therefore, renew the diplomatic relations that once obtained between our fathers, and let us transmit this heritage to our children.
These are their names: the eldest was Ujur, the second Tauris, the third Avar, the fourth Uauz, the fifth Bizal, the sixth Tarna, the seventh Kozar, the eighth Janur, the ninth Bulgar, the tenth Sawir.
[The Byzantines and Arabs hoped to stop the raids of the Khazars by converting them and later make them allies through shared faith.]
But the King-may his soul be bound up in the bundle of life [a standard burial phrase for Jews] With the Lord his God-being wise, sent for a learned Israelite.
If that God in whom I trust, and in the shadow of whose wings I find refuge, will aid me, He can give me without labor the money, the gold, and the silver which you have promised me.
Then Bulan sent for and brought from all places wise men of Israel who interpreted the Torah for him and arranged the precepts in order, and up to this very day we have been subject to this religion.
Since that day, when my fathers entered into this religion, the God of Israel has humbled all of their enemies, subjecting every folk and tongue round about them, whether Christian, Muslim, or pagan.
Alongside the river dwell many tribes in cities and towns, in open as well as fortified places.... Bear in mind that I dwell at the delta of the Itil and, by God's help, I guard the mouth of the river and do not permit the Rus who come in ships to enter into the Caspian so as to get at the Muslims.
I have to wage war with them, for if I would give them any chance at all they would lay waste the whole land of the Muslims as far as Baghdad... You have also asked me about the place where I live.
From the month of Nisan [March–April] on we leave the city and each one goes forth to his vineyards, fields and to his work... You mention in your letter that you yearn to see my face.
Abraham ibn Daud of Toledo, in his Book of Tradition (1161), writes: "You will find the communities of Israel spread abroad... as far as Dailam and the river Itil where live Khazar peoples who became proselytes.