Redmine

I'm getting the following error when I click on the "Send a test email" in the admin|email notification section.

An error occurred while sending mail (500 5.3.3 Unrecognized command)

The production.log file looks okay...

TRACE BEGIN
Processing AdminController#test_email (for 127.0.0.1 at 2008-09-03 10:46:55) [GET]
Session ID: f3dd1758e445ebb4f7bb41202162878e
Parameters: {"action"=>"test_email", "controller"=>"admin"}
Redirected to http://our.company.com/settings/edit?tab=notifications
Completed in 0.04995 (20 reqs/sec) | DB: 0.00000 (0%) | 302 Found [http://our.company.com/admin/test_email]

Processing SettingsController#edit (for 127.0.0.1 at 2008-09-03 10:46:55) [GET]
Session ID: f3dd1758e445ebb4f7bb41202162878e
Parameters: {"action"=>"edit", "controller"=>"settings", "tab"=>"notifications"}
Rendering template within layouts/base
Rendering settings/edit
Completed in 0.09460 (10 reqs/sec) | Rendering: 0.08727 (92%) | DB: 0.00000 (0%) | 200 OK [http://our.company.com/settings/edit?tab=notifications]
TRACE END

Here is the SMTP setting in config/environment.rb:

1. SMTP server configuration
   config.action_mailer.smtp_settings = {
   :address => "our.comany.com",
   :port => 25,
   :domain => "our.company.domain",
   :authentication => :login,
   :user_name => "xxxx",
   :password => "xxxx",
   }

config.action_mailer.perform_deliveries = true