Email NDR Code Meanings

What is an NDR?

NDR stands for non-delivery report. When an email is rejected from an email server you may receive an NDR email, this usually happens because you have sent the email to an email address that does not exist.

This list of NDR codes and what they mean may help you for diagnosing your email issues, or issues with your exchange or Linux based email servers.


4.2.2 The recipient has exceeded their mailbox limit. It could also be that the delivery directory on the Virtual server has exceeded its limit. (Default 22 MB)
4.3.1 Not enough disk space on the delivery server. Microsoft say this NDR maybe reported as out-of-memory error.
4.3.2 Classic temporary problem, the Administrator has frozen the queue.
4.4.1 Intermittent network connection. The server has not yet responded. Classic temporary problem. If it persists, you will also a 5.4.x status code error.
4.4.2 The server started to deliver the message but then the connection was broken.
4.4.6 Too many hops. Most likely, the message is looping.
4.4.7 Problem with a timeout. Check receiving server connectors.
4.4.9 A DNS problem. Check your smart host setting on the SMTP connector. For example, check correct SMTP format. Also, use square brackets in the IP address [] You can get this same NDR error if you have been deleting routing groups.
4.6.5 Multi-language situation. Your server does not have the correct language code page installed.
5.0.0 SMTP 500 reply code means an unrecognised command. You get this NDR when you make a typing mistake when you manually try to send email via telnet.
More likely, a routing group error, no routing connector, or no suitable address space in the connector. (Try adding * in the address space)
This status code is a general error message in Exchange 2000. In fact Microsoft introduced a service pack to make sure now get a more specific code.
5.1.x Problem with email address.
5.1.0 Often seen with contacts. Check the recipient address.
5.1.1 Another problem with the recipient address. Possibly the user was moved to another server in Active Directory. Maybe an Outlook client replied to a message while offline.
5.1.3 Another problem with contacts. Address field maybe empty. Check the address information.
5.1.4 Two objects have the same address, which confuses the categorizer.
5.1.5 Destination mailbox address invalid.
5.1.6 Problem with homeMDB or msExchHomeServerName – check how many users are affected. Sometimes running RUS (Recipient Update Service) cures this problem. Mailbox may have moved.
5.1.7 Problem with senders mail attribute, check properties sheet in ADUC.
5.2.x NDR caused by a problem with the large size of the email.
5.2.1 The message is too large. Else it could be a permissions problem. Check the recipient’s mailbox.
5.2.2 Sadly, the recipient has exceeded their mailbox limit.
5.2.3 Recipient cannot receive messages this big. Server or connector limit exceeded.
5.2.4 Most likely, a distribution list or group is trying to send an email. Check where the expansion server is situated.
5.3.0 Problem with MTA, maybe someone has been editing the registry to disable the MTA / Store driver.
5.3.1 Mail system full. Possibly a Standard edition of Exchange reached the 16 GB limit.
5.3.2 System not accepting network messages. Look outside Exchange for a connectivity problem.
5.3.3 Remote server has insufficient disk space to hold email. Check SMTP log.
5.3.4 Message too big. Check limits, System Policy, connector, virtual server.
5.3.5 Multiple Virtual Servers are using the same IP address and port. See Microsoft TechNet article: 321721 Sharing SMTP. Email probably looping.
5.4.0 DNS Problem. Check the Smart host, or check your DNS. It means that there is no DNS server that can resolve this email address. Could be Virtual Server SMTP address.
5.4.1 No answer from host. Not Exchange’s fault check connections.
5.4.2 Bad connection.
5.4.3 Routing server failure. No available route.
5.4.4 Cannot find the next hop, check the Routing Group Connector. Perhaps you have Exchange servers in different Routing Groups, but no connector.
5.4.6 Tricky looping problem, a contact has the same email address as an Active Directory user. One user is probably using an Alternate Recipient with the same email address as a contact.
5.4.7 Delivery time-out. Message is taking too long to be delivered.
5.4.8 Microsoft advise, check your recipient policy. SMTP address should be
5.5.0 Underlying SMTP 500 error. Our server tried ehlo, the recipient’s server did not understand and returned a 550 or 500 error. Set up SMTP logging.
5.5.2 Possibly the disk holding the operating system is full. Or could be a syntax error if you are executing SMTP from a telnet shell.
5.5.3 More than 5,000 recipients. Check the Global Settings, Message Delivery properties.
5.5.5 Wrong protocol version
5.6.3 More than 250 attachments.
5.7.1 Permissions problem. For some reason the sender is not allowed to email this account. Perhaps an anonymous user is trying to send mail to a distribution list.
Check SMTP Virtual Server Access Tab. Try checking this box: Allow computers which successfully authenticate to relay
User may have a manually created email address that does not match a System Policy.
5.7.2 Distribution list cannot expand and so is unable to deliver its messages.
5.7.3 Check external IP address of ISA server. Make sure it matches the SMTP publishing rule.
5.7.4 Extra security features not supported. Check delivery server settings
5.7.5 Cryptographic failure. Try a plain message with encryption.
5.7.6 Certificate problem, encryption level maybe to high.
5.7.7 Message integrity problem.

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Activate SMTP Mass Mail for Telstra Business Customers

So recently I have had the issue of our clients needing to send out mass emails and sending more emails than Telstra’s mail server will allow through (their mail servers are which is 10mb every 10 minutes. Now for clients that email in bulk (eg. Invoice runs, Newsletters, Email Marketing) this can be a problem because you may get bounce backs from Telstra’s mail servers saying that you cannot send or worse you can get your IP blocked for around 6 hours!! That means that everyone sending from that internet connection will not be able to send!!

The way to remove this restriction is through a service called “SMTP Mass Mail”. This will allow you to send over the 10mb per 10 minute limit that is offered through Telstra’s standard mail servers. There is no limit on the amount of emails sent through this server the only limit is that your emails must not exceed 20mb per email.

This sounds like something simple that you should be able to activate just by calling someone at Telstra, but it is not that simple because it seems most people you talk to do not know what the SMTP Mass Mail service is or they don’t know how to activate it. The first time I tried to activate it on an account it took about 10 phone calls to different departments and eventually I got onto somebody at technical support that knew about it and was able to steer me in the right direction.

To activate Telstra’s Mass Mailing Service you will need to call service and activations and activate it. The number for them is 13 22 53. (Or find it on this page)
If you are an enterprise customer than call the enterprise support line and talk to them about it on 1800 730 062. I have found they are a lot more helpful and the technical support people will actually know what you are talking about, then they will put you through to the sales people to process your order.

When you are on the phone with them will be able to call the client and get permission for you to talk to Telstra to make this change.

You will need the Telstra service number (Starts with a letter then full of numbers and ends in a letter)or the phone number that is attached to the email service to give them as a reference to the internet connection. The username on the ADSL service will also allow Telstra to find it.

When talking to the sales person from Telstra they may not know the process that is involved in activating this.
The process that they need to take is register a pop3 mailbox(this is at no charge to Telstra business broadband clients) that will not be used. Then they process the SMTP Mass Mailing Service from that. Make sure that they are also supplied with the correct external IP address that you are sending from.

Extra Information on SMTP Mass Mail

Mass Email is also known as
-SMTP Mass Mail Service
-Telstra Business Email

Once it is activated and you receive confirmation E-Mail saying the outgoing server should be set to this is the wrong server and may not work. You need to change outgoing Email server to:

If you need to give the customer service references to what you are talking about the following links mention the service:

-Page 17 of the Telstra Business Quick Reference Guide
-Section 16 (Page 63) of this Internet Solutions Section/Business Broadband Document

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