بسم الله الرحمن الرحيم
(Fatwa: 800/788/H=08/1437)
It is allowable to use internet to preach Islam provided it is used maintaining the limits of Shariah. However, you cannot earn the reward on preaching Islam through internet which you will be earning by struggling practically by going out in the field with sincerity according to the rules.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
