There will differences in what is considered orthodox between the Eastern Orthodox, the Oriental Orthodox, and the Assyrian Church. To give an idea of what have been the historical issues, In
1583 the Council of Constantinople with Jeremiah of Constantinople, Silvester of Alexandria, and Sophronius of Jerusalem, defined what must be professed and lived.
Baptism: Must be baptized in Orthodox style.
Church and Customs including Calendar:Must confess with heart and mouth that one is a child of the Eastern Church.
Must not wish to overthrow and destroy the dogmas and customs of the Church which have been handed down by our fathers.
Must follow the customs of the Church as the Seven Holy Ecumenical Councils decreed, and Holy Pascha, and the Menologion but
not per the Gregorian Calendar.
Must be faithful to have been taught and brought up in, and be willing to shed your bood in order to safeguard the Faith.
Filioque:Must profess that the Holy Spirit proceeds out of only the Father, essentially and hypostatically.
Mystical Supper:Must profess that the Mystery of the Holy Communion the laity must also partake of both kinds and keep the custom.
Must profess that leavened bread was used for the Mystic Supper.
Afterlife and Final Judgement:Must profess that Christ will come to judge souls together with bodies (embodied souls) not body alone.
Must profess that those repented souls of Christians who repented while in the world but failed to perform their penance, do not go to a purgatory of flame and punishment when they die.
Must profess that that hell is everlasting.
Pope:Must not profess that the Pope is the head of the Church rather than Christ.
Indulgences: Must not profess and that the Pope has authority to admit persons to Paradise with his letters of indulgence or other passports.
Must not profess that the Pope can forgive sins if such person pay money to receive from him indulgences.
orthodoxwiki.org/Sigillion_of_1583