Ibn Majah

Benefits and Issues:
Allamah Abu al-Hasan, Nur al-Din Muhammad ibn Abd al-Hadi al-Sindi (may Allah have mercy on him) writes in the margin of Sunan Ibn Majah under this hadith:
«قوله (طلقني زوجي ثلاثا) لا يدل على أن الثلاث كانت فى مجلس واحد بل قد وجد فى روايات هذا الحديث ما يدل على أنها كانت متفرقة والله أعلم»
That is, “When Sayyidah Fatimah bint Qays said that (my husband gave me three divorces), her saying this is not evidence that the three divorces (talaq) were given in a single sitting. Rather, from other narrations of this hadith, it is established that those three divorces were given separately, one after another.”

Benefits and Issues:
➊
It is understood from the narration of Sahih Muslim that the husband of Fatimah bint Qays radi Allahu anha, Abu Amr ibn Hafs ibn al-Mughirah al-Makhzumi radi Allahu anhu, had given two divorces (talaq) previously.
And the third divorce was sent from Yemen through Ayyash ibn Abi Rabi’ah radi Allahu anhu.
The three divorces were not given all at once. (Sahih Muslim, Kitab al-Talaq, Chapter: The Irrevocably Divorced Woman Has No Maintenance, Hadith: 1480)
According to this detail, many researchers have also declared this narration to be authentic because the ambiguity of this narration is removed by the narration of Sahih Muslim.
In any case, the correct ruling is that three divorces (talaq) given in one sitting will be counted as only one divorce.
For further details, see:
(The book “Three Divorces in One Sitting” authored by Hafiz Salahuddin Yusuf.)

➋
Just as divorce (talaq) can be given by addressing the woman directly, likewise, the message of divorce can also be sent through a trustworthy person, and divorce can also be sent in writing.
In every case, the divorce will take effect.