As we know, Google has excellent features – you can make yourself invisible from Gmail Inbox. No one able to see you online but you can see who is online or not.
On your IM, you found one of your friend now offline. How to ensure that is he offline or invisible from you? It’s simple. When you send any messages – if he is offline mode you will get red sentence “email@example.com is offline and can’t receive messages right now” but if he is on invisible mode – you won’t get any red words at all. So, you can easily track about your friends present mode. Enjoy