Answered according to Hanafi Fiqh by Darulifta-Deoband.com
I have sent a registered post letter of divorce to my wife in August 2013, and she received it on 9th of September 2013. I clearly stated that I divorce you and have given a genuine reason for the same. I wrote the talaq, talaq talaq three times in my letter to her.
My Question is that whether as per Islamic law is she now divorced or has the talaq been occurred? I am asking this question because I fear that her parents can bring her to my home and force me to keep her. I do not want to keep her as her parents did not tell me, before the marriage, about a mental disease she had from her teenage.

بسم الله الرحمن الرحيم

(Fatwa: 1108/1108/M=09/1435)

In the above mentioned case, when you admit that you clearly wrote talaq three times in the talaq nama which you sent to your wife. Then according to it, all the three talaqs took place on your wife and she became mughallaza baina (irrevocably divorced) and became haram for you. Now it is not lawful for both of you to live together without a valid Shariah Halalah.

Allah knows Best!

Darul Ifta,
Darul Uloom Deoband

This answer was collected from the official ifta website of Darul Uloom Deoband in India.