ActionMailer: SMTP From address may not be blank / Net::SMTPAuthenticationError Ruby / Rails Origin: Application & API Last updated 5 Nov 2026

Rails: ArgumentError: SMTP From address may not be blank: nil / Net::SMTPAuthenticationError: 535 5.7.8 Username and Password not accepted

Rails mail delivery failed — missing from, wrong SMTP settings, or rejected credentials.

Exact message you may see ArgumentError: SMTP From address may not be blank: nilArgumentError (SMTP To address may not be blank: [])Net::SMTPAuthenticationError: 535-5.7.8 Username and Password not acceptedErrno::ECONNREFUSED: Connection refused - connect(2) for "localhost" port 25Net::OpenTimeout: execution expired (smtp)
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Seen on: Ruby SMTP

Meaning

Set default from: "noreply@example.com" in the mailer or ApplicationMailer, configure config.action_mailer.smtp_settings (address, port 587, enable_starttls_auto, user, password), and use app passwords/OAuth for Gmail. raise_delivery_errors = true in development to see failures.

Common causes

  • No from address configured
  • Wrong SMTP host/port/TLS
  • Credentials missing (env vars not set)
  • Gmail needs app password
  • delivery_method not set (default :smtp to localhost)

⚡ Quick fix

  1. default from: "noreply@example.com" in the mailer
  2. Configure smtp_settings and credentials via Rails.application.credentials
  3. Test with ActionMailer::Base.mail(...).deliver_now in the console

Detailed fix by platform

Rails

  1. config.action_mailer.smtp_settings = { address: "smtp.example.com", port: 587, user_name: ENV["SMTP_USER"], password: ENV["SMTP_PASS"], authentication: :plain, enable_starttls_auto: true }

How to diagnose

  1. from — Set?
  2. SMTP — Settings correct?
  3. Auth — App password?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Application & API. Errors that are often confused with or caused by this one (click to open):

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