[1][4] According to Prof. Dr. Marek Jan Olbrycht, the letter suggests "a genuine document found by the Romans in the personal archives of Mithridates".
[4] According to Dr. Eric Adler (associate professor), the composition of the letter by Sallust, is largely the result of his own invention.
[1] Adler states that "A few scholars have asserted that the EM (Epistula Mithridatis) owes its origin to a document culled from the archives of Mithridates, which Sallust somehow acquired and translated or adapted into Latin.
Some claim that Pompey discovered this epistle in a secret archive after the Third Mithridatic War, and then presumably brought to Rome.
(...) We can be reasonably certain, then, that the EM is the creation of Sallust and is the product of a Roman historian's attempt to reconstruct the likely arguments of an anti-Roman Eastern king".