ActionMailer works for gmail/yahoo, but not for other email addresses...HELP!

I have a rails app that can send emails to gmail, yahoo accounts. But when it comes to more obscure accounts like or, the mail never arrives even though the log shows that the email was sent. Any ideas why this may be happening?

I have sent an email directly through the same web server through the command line using

mail -s and that worked. Why doesn't it work through my rails app?

here are my configuration settings (mostly default)

# Disable delivery errors, bad email addresses will be ignored   config.action_mailer.delivery_method = :smtp   config.action_mailer.raise_delivery_errors = true   config.action_mailer.perform_deliveries = true   config.action_mailer.default_charset = "utf-8"

config.action_mailer.smtp_settings = {     :address => "localhost",     :port => 25,     :domain => ""   }

help please!

thanks Tony

help! anyone?