The Christians within the Persian empire had a much better deal than many Persians. I'm thinking of the the Manichaeans, the
Zurvanites, and the Mazdakites in particular.
Here's what
Ehsan Yarshater (Columbia U) had to say about them:
We may then chart the course of the Mazdakite movement as follows. Sometime in the course of the 5th century, presumably during or soon after the reign of Bahram V, Zardusht Khurragaan, a mobad or possibly a chief mobad of Fasaa, began reform movement in Zoroastrian religion; he claimed to offer a correct interpretation of the Avesta. It is also possible that, claiming, to be an incarnation of an earlier leader, he only renewed and elaborated a movement begun previously by one Bundos, who had resided in Rome for a while and who had come under the influence of some gnostic religions there. The assigning of inner meaning to Zoroastrian scriptures early branded the followers of the movement as Zandiks.
Zardusht's interpretation of the Avesta disguised a set of beliefs, widely spread in late antiquity, which postulated a remote supreme deity and attributed the creation and management of the world to two demiurges. [The rest of this paragraph is about the religious belief of the said interpretation].
[Page 1019] We do not know how the movement fared between its inception and the time of Kavaad. We may assume that it continued to attract followers through quiet missionary work, which prefigured the Baatini da'wa. During Peerooz's reign Iran was afflicted with a number of disasters, and when he was killed in 484, during a catastrophic war with the Hephthalites, Iran was facing formidable social, economic and political problems. The coutry had been weakened by successive wars and heavy taxation, and now was subjected to the humiliation of having to pay tribute to the Hepthalites, while territory was lost to the victors and much of the army destroyed.
About this time the leadership of the sect passed to Mazdak son of Baamdaad, a man of chrisma and revolutionary temper, deeply committed to the notion of social justice and the welfare of the poor. Under his leadership te movement assumed a pronounced social colouring. Capitalizing on popular discontent, Mazdak questioned the enormous privileges of the noble classes and the clergy. He not only envisaged an egalitarian society, but as a man of action also planned to carry out his communistic ideas. The peasants, the artisans and the "have-nots", in general, welcomed his teachings and flocked to his side. His movement was called that of "justice". (However, he did not include the slaves in his scheme, else our sources would not have missed the point as grounds for further invectives against him; cf. below, p. 1024).
Whether any outside influence affected the formulation or the spread of the Mazdakite revolutionary attitude is hard to say; our sources are silent on that. [The rest of this paragraph discusses this outside influence possibility].
[Page 1020] Kavaad, a capable and ambitious king, but also a man of liberal tendencies and with a passion for justice, who resented the restricting power of the nobles and the Church, sided with Mazdak and accepted the movement's interpretation of the good religion. He promulgated a number of laws curtailing the privileges of the nobles and introducing unprecedented social reforms. The king's support gave heart to the sectarians, and disturbances resulted from the Mazdakite mob attacking granaries, storehouses, and the mansions of the affluent and their harems. The nobles reacted sharply and Kavaad was deposed.
When Kavaad returned to the throne with the help of the Hephthalites and the assistance of some of the nobles inclined to Mazdakism, he had been somewhat sobered and acted more cautiously; but there is no reason to believe that he had undergone a drastic change of heart. His acceptance of Mazdakism must have been based on religious grounds, as much as anything else, and he presumably continued his faith, even though the Mazdakites' excesses drove him gradually to agree to their restriction and finally to their suppression.
Mazdak's end and the downfall and massacre of the Mazdakites have been recounted with some element of fiction and fantasy. The Mazdakites were trying to ensure the succession of Kaavus, the elder son of Kavaad and a sympathizer, against Khusrau, Kavaad's younger and favorite son. Khusrau, who was supported by the Zoroastrian priesthood and anti-Mazdakite nobles, eventually persuaded the king to give in to his plans for putting down the sect. By this time the Mazdakite disruptions and possibly also Mazdakite mismanagement of common properties must have alienated many of their earlier supporters, and the desire for a return to law and order was probably spreading. Khusrau arranged for a typical religious debate in which the Mazdakite leader was foredoomed. Most sources mention a massacre of the Mazdakites in Ctesiphon, which apparently took place under Kavaad in about 528 but was directed by Khusrau, who was now assuming de facto royal powers. The massacre must have been followed by a wave of persecutions in the provinces, repeated again at the beginning of Khusrau's reign. The sect lost much of its following and strength, particularly since Khusrau combined his suppression of the Mazdakites with far-reaching social, administrative, and fiscal reforms, carried out with an iron hand. The sect went underground, but survived, particularly outside urban centers.
Pages 1022-1024 discusses the Mazdakite movement, and its influence on uprising against moslem invaders after the fall of the Sassanids upon the arab conquest. The most interesting statement is on page 1022, first paragraph:
With the Muslim conquest and the fall of the Sasanian state the Mazdakites resumed their activities. In the period of sever persecution under the late Sasanians the Mazdakites seem to have developed or refined a system of beliefs which we find later adopted also by the extremist Shi'is.