This is an issue of dispute. I believe that answering Salam in the written form is not mandatory.

Nowadays we hav wats app and wat app groups… So here in wats app group we get lots of wishing of Assalaamualaikum …many people wish us.. So is it mandatory to reply them back by typing it or just we say Walaikumsalaam to ourselves is enough..

Halal/Haram Matters | November 17, 2017 9:50 pm
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May I kill my goldfishes just because I hate them? I mean c’mon, they’re just useless fishes that plants when I don’t want them to.
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Sheikh i have friends at school and when I joke around with them I use like some offensive joke like I will call them a type of animal for example but they take it as a joke and laugh about it. Is this permissible if they don’t mind