Verified email not sending through Heroku/Mailgun

Question

I have Rails app on Heroku. It has a custom domain, and I've tried to set up email sending through Mailgun. I've installed Mailgun as an add-on through Heroku, and I've gone through the steps Mailgun gives to "verify" my custom domain. If I run Mailgun's "Check DNS Records Now" everything comes back green and the status is "Active." I can even send messages from my custom domain with the curl call they provide. However, when I try to send an email from my Rails app using ActionMailer I get: Net::SMTPFatalError (554 Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients in domain settings.

Why does it think I'm using a "Sandbox subdomain"? Here's what I have in environments/production.rb:

  # Mailgun
  ActionMailer::Base.smtp_settings = {                                    
    port: ENV['MAILGUN_SMTP_PORT'],                                       
    address: ENV['MAILGUN_SMTP_SERVER'],                                  
    user_name: ENV['MAILGUN_SMTP_LOGIN'],
    password: ENV['MAILGUN_SMTP_PASSWORD'],                               
    domain: 'my-custom-domain.com',                                               
    authentication: :plain,                                               
  } 
  ActionMailer::Base.delivery_method = :smtp                              
  # Devise recoverable      
  config.action_mailer.default_url_options = { host: 'my-custom-domain.com' } 

For development I'm using Gmail so I know it's reading the right config file. And all the env vars are set correctly. The from is set correctly as well, I see it my logs ([e-mail]) What did I miss? Is there something that could still be propagating even through the status is active?

Thanks!

Answer 1

1. Make sure you have verified domain set (mailgun -> domains -> verified domains & dns - all green).
2. Make sure you updated env variables in Heroku to work with verified domain (heroku -> settings -> reveal config vars) should have fields: MAILGUN_API_KEY, MAILGUN_DOMAIN, MAILGUN_SMTP_PASSWORD, MAILGUN_SMTP_LOGIN, MAILGUN_SMTP_SERVER, MAILGUN_SMTP_PORT with proper values.
3. Make sure you have cleared the list of authorized recipients (mailgun -> domains -> authorized reciepients) - so everyone can receive your emails.
4. Make sure you have cleared the list of IP whitelist (mailgun -> account overview -> account settings -> security -> IP whitelist) or included ip of your heroku app. In my case the only ip there was my localhost ip (for dev) and it was blocking heroku deployed app for sending emails.

Answer 2

So the issue turned out to be that when I verified my custom domain it created a second domain under my Heroku/Mailgun account. I still had the credentials from the xxx.mailgun.org (sandbox) domain in my Heroku env vars. Once I replaced them with the credentials from my custom domain everything worked. (Since Heroku set the first set of env vars I foolishly assumed the new set would get put in automatically.) Sigh...

Thanks for your help lyen.

Answer 3

Did you add the recipients of your e-mail to "Authorized Recipients" list under https://mailgun.com/app/domains/sandbox_your_domain.mailgun.org?

Be sure to add a real e-mail address which can receive e-mails.

This is because mailgun would send a confirmation e-mail asking if the owner of the e-mail address really wants to receive e-mails from mailgun.

Answer 4

To add on to lostphilosopher answer, I recently solved this MailGun custom domain issue myself.

Here's what worked for me:

Situation: After successfully adding a custom domain to Mailgun, my mail sending/receiving stopped working

Errors: After adding custom domain and verifying DNS with Mailgun, I received error messages such as:

Net::SMTPFatalError: 554 Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients in Account Settings.

Solution: Realize that Heroku does NOT automatically update configuration variables for you. You must manually update them with values for your new domain.

1. In MailGun - Find your new MailGun domain settings under under https://mailgun.com/app/domains
2. In Heroku - goto: Heroku > App > Settings > Reveal Config Vars
3. In Heroku - Update the following config vars
   • MAILGUN_DOMAIN
   • MAILGUN_SMTP_LOGIN
   • MAILGUN_SMTP_PASSWORD

And yes I agree - MailGun docs are not the most thorough. Especially when it comes to testing your setup.