Firestore通过gmail而不是sendgrid发送邮件

Question

我想在firestore中进行新预订时发送邮件，其中有一些数据用于测试目的，它现在只有firstName，lastName和email，但这并没有改变一件事。这应该发送一个文件在firestore中创建一个文件，但是它给了sendgrid但是我怎么能用gmail而不是sendgrid来改变呢？

import * as functions from 'firebase-functions';
import * as admin from 'firebase-admin';
import * as sgMail from '@sendgrid/mail';

admin.initializeApp(functions.config().firebase);

const SENDGRID_API_KEY = functions.config().sendgrid.key;
sgMail.setApiKey(SENDGRID_API_KEY);

exports.firestoreEmail = functions.firestore
  .document('reservations/{reservationId}')
  .onCreate(event => {
    const reservationId = event.params.reservationId;
    const db = admin.firestore();

    return db.collection('reservations').doc(reservationId)
      .get()
      .then(doc => {
        const reservation = doc.data();

        const msg = {
          to: reservation.mail,
          from: 'my-email@gmail.com',
          templateId: 'my-key',
          substitutionWrappers: ['{{', '}}'],
          substitutions: {
            firstName: reservation.firstName,
            lastName: reservation.lastName
          }
        };
        return sgMail.send(msg)
      })
      .then(()=> console.log('email sent!'))
      .catch(err => console.log(err))
  });

为了测试这个，我在我的firestore db中创建了一个新的预订

如何使用gmail而不是sendgrid来发送邮件，还是有其他方式我可以从客户端发送邮件，因为没有可能的后端？