Zoroastrianism originated in Iran. It was the official religion there in some form or other until the Muslim invasion.
The Zoroastrians in India are called Parsees. The Parsees were refugees from the Islamic conquest. The Indian rulers there allowed them to remain in India under the precondition that they agree not to proselytize. This became a tenet of Parsee Zoroastrianism as a consequence. The Parsees hold that to whatever religion one was born that was the relgion they were fated to serve and a person could be saved by being a good person in any religion.
I think the Zoroastrian community in Iran, the few that may still exist, do not believe in not accepting converts. I have read on the internet that some Zoroastrian communities accept them.
This issue of not accepting converts is a curious and contradictory one. Zoroaster himself started out in a world dominated by pagans and he converted a great many of them. Others people were converted along the way as time went on. The Zoroastrian Community worldwide is suffering from a diminishing population. It would seem to me that seeking out converts and accepting them is the only way for a religion, certainly a religion of so few followers, to remain and grown.