Hi Ray,
How is your program sending the emails?
Does it do an MX lookup and try to send directly?
Does it connect to a specific SMTP server for outgoing relay?
Is it following however the server it's on is configured?
Once you know how it's sending, you'll be able to go to that server and check the mail logs to see what's happening to the emails.
If everything looks good there, continue following each hop from source to destination until you find the problem.
to Email Questions!