session data getting stored every time

Below is the API that basically stores data in session if not already present then returns an empty JSON, otherwise sends the session data stored corresponding to that mail:

app.use('/session', function(req, res) {
  if (req.body.email in req.session) {
    console.log("user data already available");
    res.send(req.session[req.body.email]);
  } else {
    req.session[req.body.email] = {};
    req.session[req.body.email]["email"] = req.body.email;
    req.session[req.body.email]["gender"] = req.body.gender;
    req.session[req.body.email]["dbname"] = req.body.dbname;
    console.log("user session stored");
    res.send({});
  }
});

Below is the ajax call that I am making from my application. It is a cross domain call and I have set the response header accordingly.

$.ajax({
    url: 'url/session',
    type: "POST",
    crossOrigin: true,
    data: {
      "email": "email",
      "gender": "all",
      "dbname": "dbname"
    },
    success: function(data) {
      console.log("inside session api call success");
      console.log(data)
    }
    });
});

Now the problem is that if I hit the API using postman, it works fine but when I use that in my application, it overwrites the session every time and returns empty json. What am I doing wrong?

edit : Figured out that each time ajax call is happening, past session data gets deleted for all emails ids.session value gets reset but still unable to figure out why this is happening.