We have family in several different countries. For the most part all our communication is online. I do not have postal addresses for most of them.
I have sent online condolences when former classmates family members have died too. I have not seen these people for over 30 years, but want to acknowledge their loss.
I know there is a generation that feels only hand written communication is meaningful. That is what was taught when they were growing up. But even then, a telegram received at a wedding or funeral was considered a very special and extravagant gesture.
Email, online condolences etc have only been around a short time, but they are to this 40 something valid forms of communication.