I installed and configured exception notifier to be notified of any unexpected errors in our production environment. At first i tried this out in development, used gmail as my smtp server and all was working fine. My action mailer configuration looked as follows, in environment.rb: [ruby] # configure mailing config.action_mailer.delivery_method = :smtp config.action_mailer.smtp_settings = { :enable_starttls_auto => true, :address => "smtp.gmail.com", :port => "587", :domain => "localhost", :authentication => :plain, :user_name => "<snipped>", :password => "<snipped>" } ExceptionNotifier.exception_recipients = %w(bla@my_clients_domain.com) ExceptionNotifier.sender_address = %("<snipped>@gmail.com") ExceptionNotifier.email_prefix = "[My Application ERROR] " [/ruby] Using this configuration worked, and i received the e-mails. Alas, as usual, on my client's production server the port to reach gmail was blocked, and when i asked to open it, they instead proposed to use their own smtp-server. So i changed the configuration as follows: [ruby] config.action_mailer.smtp_settings = { :address => "192.168.0.10", :port => "25", :domain => "production-domain.be", :authentication => nil } ExceptionNotifier.exception_recipients = %w(bla@my_clients_domain.com) ExceptionNotifier.sender_address = %("info@production-domain.com") ExceptionNotifier.email_prefix = "[My Application ERROR] " [/ruby] The first thing i did wrong was the domain-name. At first i wrote "@production-domain.be" in my action-mailer configuration, so my HELO request was blocked. Secondly, apparently, because i wrote ExceptionNotifier.sender_address = %("info@production-domain.com") the sender address was not recognised and the mail was rejected by our own SMTP-server. This took me a while to figure out. Luckily our sys-admin noticed the difference. The fix: [ruby] ExceptionNotifier.sender_address = %(info@production-domain.com) [/ruby] And now i know for sure that if i get no mails, my application really is working :)