Mailgun or Sendgrid - 501 Username used for auth is not valid

Question

I am trying to send email with mailgun (or Sendgrid enter code here ) and receiving this error:

Net::SMTPAuthenticationError (501 Username used for auth is not valid email address

My setup is as simple as it should be:

  config.action_mailer.smtp_settings = {
     :user_name => ENV['MAILGUN_SMTP_LOGIN'], 
     :password => ENV['MAILGUN_SMTP_PASSWORD'],
     :domain =>  'mydomain.co'
     :address => ENV['MAILGUN_SMTP_SERVER'],
     :port => ENV['MAILGUN_SMTP_PORT'],
     :authentication => :plain,
     :enable_starttls_auto => true
   }

Any idea?

Answer 1

It seems like some custom code logic (we use Jumpstarter for Rails) was overriding settings in production.rb file.

The most helpful thing in my case was to take a look at rails c (on production) and then run:

ActionMailer::Base.smtp_settings

I immediately noticed that settings were not identical to those I specified. Then it was easy to find where the real issue was.