Nodemailer with Gmail service not working on heroku

I believe this is an issue with google account security.

• Google blocked your sign-in to use the mailing features due to an unknown device (location).

A few step to verify this:

• Start your server locally and sends the email.

• Check your account alerts for unknown sign-in.

This can be temporally resolved by:https://accounts.google.com/DisplayUnlockCaptcha

A more permanent resolution would be to change your password to a stronger level:

upper case letter + lower case letter + special symbols + numbers

Instead of using direct gmail credentials like this

auth: {    user: 'foobar@gmail.com',    pass: 'foobar'}

Use OAuth2

 auth: {    type: 'OAuth2',    user: 'user@example.com',    accessToken: 'ya29.Xx_XX0xxxxx-xX0X0XxXXxXxXXXxX0x'}

Google blocks the heroku IPs (unsafe), if we are using direct credentials like you mentioned above. You can refer this Medium article here

5 years later, I still struggled this problem (all answers found on SO failed in my case). Here is what I did, for now everything works smoothly:

• Install SendGrid addon to your Heroku app (Free plan gives you 12k messages a month)
• Go to SendGrid panel
• Go to Marketing -> Senders to add your sender bot, configure it like this:
• From = any_address@heroku.com
• Reply = your_gmail@gmail.com

• Generate API KEY here

• Configure NodeMailer like so:

    const nodemailer = require('nodemailer'),      sgTransport = require('nodemailer-sendgrid-transport');  const mailTransporter = nodemailer.createTransport(sgTransport({      auth: {          api_key: process.env.ADMIN_EMAIL_API_KEY // your api key here, better hide it in env vars      }  }))

• To send an email now, you have to add your gmail in 'Reply To' field, like so:

    mailTransporter.sendMail({      from: `"Admin" <any_address@heroku.com>`,      to: 'receiver@hotmail.com',      replyTo: 'your_gmail@gmail.com',      subject: 'Something',      html: `Boom !`  });

I think that's all, in case I forgot something, please add a comment below