which system does that? neither telegram, nor whatsapp do it, and it annoys the hell out of me. at least whatsapp tells me that the sender doesn't get a notification until i respond or add the contact. wechat actually requires a connection request before allowing you to message someone, with all the complaints about privacy, wechat has the better UX to avoid getting spammed, linkedin requires a connection too, if you don't have a pro account. i don't know about any others.