After Khosrau II's attempt to eradicate the Exilarchs, the Jews were led by a [http://www.jewishencyclopedia.com/articles/10222-ma-amad Mahmud] which attempted to secure themselves in Edessa leaving the Jews with no public Exilarch again until Bostenai was installed by the lapsed Gnostic Umar I following Umar's eviction of Traitors from Arabia.
Ma'amad, pronounced Mahamad, (or Mahmud in [https://en.wikipedia.org/wiki/Al_Anbar_Governorate Tachkastan] and Muhmad and Mehmet) is the name given to a Jewish Counsel charged with governing a community of Jews and Noahites. The Counsel may be one person or consist of several members. Each member of the Ma'amad is addressed as Ma'amad. Each Ma'amad appoints its own successor (Khalifah).