let endpoint = function(app) {
  app.post('/send-mail', function(req, res) {
    sgMail.setApiKey(process.env.VUE_APP_APIKEY);
    sgMail
      .send(req.body)
      .then(() => {
        // do something
      })
      .catch(error => {
        // do something
      });

    return res.send(req.body);
  });
};

MY_VAR=my_value node server.js

VUE_APP_APIKEY=[API KEY VALUE]

require('dotenv').config()