Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

For a project that I have been assigned to, I need to send emails to a business partner ( from one production server. However, my emails neither reach their destination nor bounce back to me ("reject: MAIL from unknown").

Further analysis by my IT support shows that emails are successfully sent out ("Message accepted for delivery").

The app I coded is not using a public internet email address (e.g. to send these notifications. Instead, it uses an intranet email address (the server's where my code resides:

My IT support guys believe it is the cause of the problem.

We created an alias but it made no change. Would adding my public internet email address to "trusted-users" file (we use sendmail) help?

How can I solve this?

share|improve this question
up vote 1 down vote accepted

It is probably because when you e-mail, your e-mail server announces, who it is. The receiving server then does a reverse DNS check by comparing the name of the server your e-mail server announced with the PTR (reverse DNS record) of the IP addresses the inbound mail is coming from. If they do not match, many e-mail servers just drop them without any bounce messages.

I would suggest that you go test it here:

If you do not hae a PTR record, you have two choices:

  1. Get your ISP to add it.
  2. Use a smarthost to relay mail through.
share|improve this answer
Mmm...makes sense to me. I did not include snapshots of my maillogs but it seems to confirm with you stated. I believe sendmail can work with a smarthost. I'll look into it. – Chris Jul 27 '11 at 18:33
Accepted your answer. Although I could not vote it up since I have only 8 rep. – Chris Jul 27 '11 at 18:41
@Chris Thank you very much. I am maxed for today with upvotes anyway, so I only get the points for marking anyway, so that was great. I really appreciate it. – KCotreau Jul 27 '11 at 18:43

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.