actionmailer issues...any experts?

I have a rails app that can send emails to gmail, yahoo accounts. But when it comes to more obscure accounts like emailme@my-app.com or emailme@blah.edu, 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 => "my-app.com"   }

help please!

thanks Tony