No NDR for invalid addresses on specific domain

Posted on 2011-05-11
Last Modified: 2012-05-11
Our company is having issues receiving proper NDR's from invalid e-mail addresses on a specific domain. For example, using a fake address like will not send a reply to us that the address is invalid. This works sending from other e-mail servers such as Gmail and Hotmail.

Looking at our message tracking center in Exchange 2003 shows the test messages being transferred to what looks like a proxy on their end (they are a Taiwan domain), but the message tracker ends there.
Question by:dcgagne
    LVL 22

    Accepted Solution

    Most likely the receiving domain is set not to send NDR. This is one way of preventing a dictionary attack, but is not a particularly good one since it ignores RFC conventions.

    If you want to see what is actually happening try a manual telnet session on port 25 to the recipient's MX server.

    Author Comment

    Unfortunately, the external domain has telnet access blocke, so testing to them is limited. If it helps, here is the error message from a gmail box when trying to send to that non-existent address:

    Delivery to the following recipient failed permanently:

        [e-mail address redacted]

    Technical details of permanent failure:
    Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 500 500 5.0.0 Service unavailable (state 18).
    LVL 22

    Expert Comment

    by:Brian B (TBone2K)
    You can't block telnet per se, you block the port that telnet uses. In the case of SMTP it is 25. So if you can't reach them on port 25, there is your problem. Their server doesn't conform to standards, therefore you can't communicate with it.

    The GMail error is a similar story. The service on the reipient's server is not working.

    No matter what, I am sure this has nothing to do with your system.

    Author Comment

    Thanks, I was sure we were fine on our end but I needed to cover all my bases.

    Featured Post

    Why do Marketing keep bothering you?

    Is your marketing department constantly asking for new email signature updates? Are they requesting a different design for every department? Do they need yet another banner added? Don’t let it get you down! There is an easy way to manage all of these requests...

    Join & Write a Comment

    Create high volume marketing opportunities using email signatures with these top 10 DOs and DON'Ts of email signature marketing.
    Check out this infographic on what you need to make a good email signature that will work perfectly for your organization.
    In this video we show how to create an email address policy in Exchange 2013. We show this process by using the Exchange Admin Center. Log into Exchange Admin Center.:  First we need to log into the Exchange Admin Center. Navigate to the Mail Flow…
    The video tutorial explains the basics of the Exchange server Database Availability groups. The components of this video include: 1. Automatic Failover 2. Failover Clustering 3. Active Manager

    746 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    14 Experts available now in Live!

    Get 1:1 Help Now