This questions has reminded me of something, an affair that is well known amongst the people of knowledge, but it is now [asked] a wide spread - it is;
If someone writes something to me, even if it were by phone; whether it is a text or a WhatsApp message or otherwise, and writes the Salam to me, is it an obligation upon me to respond to the Salam?
The Answer is yes, it is an obligation to respond to his Salam.
Ok, how do I respond to his Salam?
The obligation is that you respond verbally. If I receive a message, even if it were by phone, that reads; ‘As Salam ‘Alaykum.’
I must respond saying; ‘Wa ‘Alaykum as-Salam.’
If it says; ‘As-Salam ‘Alaykum wa Rahmatullah.’
I respond; ‘Wa ‘Alaykum as-Salam wa Rahmatullah’, or I add; ‘wa Barakatahu.’
It is Mustahab (recommended) to respond in written form, it is Mustahab – for perfection. According to the preponderant opinion amongst the people of knowledge; that you write back in the text wa alaykum as-Salam wa Rahmatullah for example, [is Mustahab]. Yes, some of the people of knowledge obligated this, but this opinion needs to be reconsidered.
It is from perfection [Mustahab] to write it,
The obligation is to respond verbally.
We need this a lot now, when we receive text messages beginning with Salam, it is indeed an obligation that you respond. Some people think that since the other person cannot hear you, you do not need to respond to the Salam.
No, this is wrong, as long as he gave you the Salam and it has reached you, say; ‘Wa ‘Alaykum as-Salam’ as an obligation. And if you write it back to him, then this is from perfection.