Check if user mail is online on gmail

[Amit Shef]

Hello.

My question is how can i know on gmail if the user is online?

I know there is GMail API and JavaMail API but still don't know how to do it.

Thanks in advance.

[Ulf Dittmer]

JavaMail definitely has nothing in this regard. It seems more a function of Hangout or Chat. But many people don't like to advertise whether they're online or not, so it's possible there's nothing in the API.

[Karthik Shiraly]

By user is "online", are you referring to gtalk chat status? If so, the term you are looking for is "presence API" and the technologies to search are XMPP and Jabber.
Do a quick test of whether google announces presence to XMPP clients using an android XMPP app like Xabber or a desktop app like pidgin (last time I used pidgin, it did support, but that was couple of years ago).
If they show presence of your contacts correctly, then it's confirmed that google supports presence notifications over XMPP.
You can then implement the same in your own app using some 3rd party XMPP library.