Although Zoroastrianism is not an Abrahamic religion and so the "Magians" of the Quran are not counted with Jews and Christian, in practice Zoroastrians were treated as sort of semi-dhimmis. The "semi" here is less a reflection of theology and more one of politics and security.

In the traditional Zoroastrian heartland, modern-day Iran and Iraq, Zoroastrianism was the imperial religion. While rural areas had been slowly converting to versions of Christianity and Judaism over the course of late antiquity, the aristocracy and imperial leadership was inseparable from Zoroastrianism; it was the imperial ideology.

So as Muslim armies swept in and established an Islamic administration, a couple things happened. Zoroastrians were allowed to maintain their houses of worship, religious practices, etc. There weren't enormous massacres or campaigns of forced conversion.

On the other hand, the Zoroastrian leadership of the Sassanids was swiftly dismantled. Those people faced a real choice of conversion or sudden obscurity. Conversion had its secular benefits. Al-Afshin had been an Iranian prince, but as a Muslim convert, he became a famous general of the Abbasid army.

Early Islam, too, inculturated a lot of Iranian-Persian culture, which helped make conversion more palatable. Even after the economic and political gains. Muslims were pragmatic, too: they often waived the requirement of circumcision for wary adult male converts. The cities of the former Sassanid Empire saw conversion to Islam fairly quickly, though Zoroastrianism hung on in more rural territories through the 10th and 11th century.

There are still pockets of it today, as noted elsewhere in this thread, but it had already been in decline as a faith outside the imperial hierarchy even before the advance of Islam. The Abbasids' adoption of so much else in Iranian culture and the attraction of participating in Muslim trade networks, armies, and civic life made conversion to Islam quickly attractive for the elite, even if Zoroastrianism itself was not banned.

Major source here is Jonathan Berkey, The Formation of Islam.

"Dhimmis were required to wear special clothes", "dhimmis weren't allowed to ride animals (lol)"

"the first 8 centuries after Islam was founded were basically just looting and plundering surrounding areas until they converted to Islam".

I made a very lengthy rebuttal to the poster of these comments only to find it had already been deleted. I fucking love this subreddit and it's moderation team/standard. As someone who is very passionate and informed on the complex history of Islam, this sub is the one bastion of hope for me on this site and the frankly one of the few reasons I peruse reddit these days. Never change /r/Askhistorians.

And for the record /u/IamaHistorian is most assuredly not.

I know this isn't a post in regards to the topic but I just had to show my appreciation.