ActionMailer settings incorrectly differing between development and production

The Error

I've got my ActionMailer setup and working perfectly in development. I can call UserMailer.welcome(user).deliver, and the email reaches its destination. However, when I push my code into production and call the same deliver method, suddenly I get an error:

Errno::ECONNREFUSED: Connection refused - connect(2)
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:546:in `initialize'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:546:in `open'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:546:in `tcp_socket'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:555:in `block in do_start'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/timeout.rb:58:in `timeout'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/timeout.rb:89:in `timeout'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:555:in `do_start'
    from /usr/local/rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/net/smtp.rb:525:in `start'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/gems/mail-2.3.0/lib/mail/network/delivery_methods/smtp.rb:128:in `deliver!'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/gems/mail-2.3.0/lib/mail/message.rb:1989:in `do_delivery'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/gems/mail-2.3.0/lib/mail/message.rb:230:in `block in deliver'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/actionmailer/lib/action_mailer/base.rb:414:in `block in deliver_mail'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/activesupport/lib/active_support/notifications.rb:55:in `block in instrument'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/activesupport/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/activesupport/lib/active_support/notifications.rb:55:in `instrument'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/actionmailer/lib/action_mailer/base.rb:412:in `deliver_mail'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/gems/mail-2.3.0/lib/mail/message.rb:230:in `deliver'
    from (irb):10
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/railties/lib/rails/commands/console.rb:45:in `start'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/railties/lib/rails/commands/console.rb:8:in `start'
    from /webapps/myapp/production/shared/bundle/ruby/1.9.1/bundler/gems/rails-5680a51dcbaf/railties/lib/rails/commands.rb:40:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

The Problem Thus Far

Probably the most valuable info I can offer is that the actual delivery_method data on the Message object is incorrect in production. In development, when I call UserMailer.welcome(user).delivery_method, the (formatted) output is:

#<Mail::SMTP:0x000001042c4a20 @settings={
  :address=>"smtp.gmail.com",
  :port=>587,
  :domain=>"foobar.com",
  :user_name=>"example@foobar.com",
  :password=>"MY_PASSWORD",
  :authentication=>"plain",
  :enable_starttls_auto=>true,
  :openssl_verify_mode=>nil}>

This clearly matches the settings I've defined in mailers.yml. In production, when I make the same call, the output is:

#<Mail::SMTP:0xbfb2c18 @settings={
  :address=>"localhost",
  :port=>25,
  :domain=>"localhost.localdomain",
  :user_name=>nil,
  :password=>nil,
  :authentication=>nil,
  :enable_starttls_auto=>true,
  :openssl_verify_mode=>nil}>

This just appears to be the defaults as defined on line 22 of ActionMailer::DeliveryMethods instead of my own settings from mailers.yml.

Relevant Code

As far as I can tell, my environments should have ActionMailer setup the same.

config/environment.rb:

Myapp::Application.config.action_mailer.delivery_method = :smtp
Myapp::Application.config.action_mailer.smtp_settings = YAML.load_file(
    Rails.root.join('config', 'mailers.yml'))[Rails.env].to_options

config/mailers.yml:

default: &default
  address:              smtp.gmail.com
  port:                 587
  domain:               foobar.com
  user_name:            example@foobar.com
  password:             MY_PASSWORD
  authentication:       plain
  enable_starttls_auto: true

development:
  <<: *default

production:
  <<: *default

config/environments/development.rb:

Myapp::Application.configure do
  # ...
  config.action_mailer.raise_delivery_errors = false
  config.action_mailer.default_url_options = { :host => 'localhost:3000' }
  config.action_mailer.interceptors = ['MailInterceptor']
  # ...
end

config/environments/production.rb:

Myapp::Application.configure do
  # ...
  config.action_mailer.default_url_options = { :host => 'foobar.com' }
  # ...
end

Note that I've also tried commenting out the two extra lines in development.rb (and tried adding them into production.rb) with no change -- I still get the same error in production, but not development.

Also, although I don't think it's relevant, I'll include MailIntercepter that I reference in development.rb (it's just to redirect all mail to my email address instead of test users' email addresses):

class MailInterceptor
  def self.delivering_email(message)
    message.subject = "[#{message.to}] #{message.subject}"
    message.to = "example+catcher@foobar.com"
  end
end