I am using Rails Mailer and Gmail to send emails. But I keep getting the Net::SMTPAuthenticationError 535-5.7.8 Username and Password not accepted error.

I checked out other questions regarding this problem but unfortunately, they didn't help.

I have a 2-step authentication enabled and I did create the App Password for my Rails app.

This is my configuration in production.rb:

  config.action_mailer.perform_caching = false

  config.action_mailer.delivery_method = :smtp
  host = 'myhost'
  config.action_mailer.default_url_options = { host: host }

  config.action_mailer.smtp_settings = {
    address: 'smtp.gmail.com',
    domain: 'myhost',
    port: 587,
    user_name: 'myemail@domain.com',
    password: ENV['GMAIL_APP_PASSWORD'],
    authentication: 'plain',
    enable_starttls_auto: true
  }

Now, it is worth noting that I am using a non-Gmail address but I am using GSuite which allows me to log in to Gmail with that address and use it pretty much as a Gmail address.

If it means anything, after trying to send an email with Rails I did receive an email about Blocked login alert. And to note again, I am using the App Password, not the general password for the account.

Seen some answers saying that I have to enable less secure apps option but I can't enable it while 2-step is active.

Less secure apps

Have you allowed for less secure apps? Please do so, and see if that helps. Less secure apps

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2fa use an app password.

If using 2 Step Verification in Gmail, you may need an application password. Create & use App Passwords

Xoauth2

If it still doesnt work you may need to consider checking xoauth2-protocol