Answer
(Fatwa: 761/587/D=1431)
It is unlawful to marry a woman whom one has divorced thrice, neither within iddah period nor after it, until legal halalah does not take place. The method of halalah is that a woman divorced with three talaqs will marry any other man after completing her iddah period and that man after having intercourse divorces her or dies, only then after completing her iddah period it will be lawful and possible for this woman to marry her first husband.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband