Hello Alex, I have already consulted my lawyer friend, and he told me the same thing. In my former O&G company, email is allowed in court. In fact, any media we use to communicate can be binding in court. Therefore, we can`t call whatsApp/WeChat/voice that we don`t want to say. So be very careful. I think it is mandatory by default, without being mentioned in the Treaty. The contract did not say that the “only” acceptable form of termination is by letter. However, if we include electronic media as an acceptable form of communication, we must add an additional clause to hold both parties to account, to inform if the number/ID changes. The standard rental agreement is for informational purposes only and does not constitute legal advice from us.