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!


help! anyone?