Countries that do not require a Iran visa are Syria, Turkey, Lebanon, Azerbaijan, Georgia, Bolivia, Armenia, and Egypt.

iran visa
Citizens of the countries including United state, United kingdom, and Canada only can acquire Visa if they travel to Iran with a tour. The tour program should define and confirm for the Citizens from these countries and during the tour, any change should be reported.
Citizenship which can not have airport visa are United state, United kingdom, Canada, Iraq, Columbia, Jordan, Somalia, Afghanistan, Pakistan, Sri Lanka, India, and Bangladesh. They should apply for the visa through Iran embassy or Consulate.
Citizenship which can not acquire Iran visa reference code from the agencies are Bangladesh and Afghanistan. they should apply for the visa through Iran embassy or Consulate.