Bounced Email

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If you are unable to send email to a "" recipient or you have been told that your email is being rejected by your account, please consult this documentation.

What is DNS?

Every website, email account, etc., on the Internet is hosted on at least one computer server that has a unique numeric IP (Internet Protocol) address. To access a particular Internet service, you have to specify its IP address. However, because numbers are difficult to remember, an easier, alphabetic host name or domain name can be associated or "mapped" with an IP address. DNS (Domain Name Service) is the Internet directory service that stores IP addresses and maps them to their host names, allowing you to use the host name to access your Internet service. For example, instead of having to remember buddy@ to send email to your friend, you can simply use When Internet Service Providers (ISPs) looks up the IP address to see the host name, the process is called Reverse DNS.

Bounced Email and Reverse DNS

In an effort to control Unsolicited Bulk E-mail (also know as SPAM) many Internet Service Providers have begun to require reverse Domain Name Service (DNS) lookup. This process verifies the identity of an e-mail server attempting to send e-mail to someone within a domain such as The standard for e-mail processing requires that a reverse lookup exist for each piece of e-mail, but this standard is not always enforced by mail servers. However, URI, along with the Internet Service Providers (ISPs) for many business and universities, has begun enforcing this requirement.

Many SPAMers attempt to shield their identity by using an e-mail server that does not have a reverse lookup entry, they may even spoof domain text addresses. E-mail "servers" that cannot be identified through Reverse DNS lookup are typically zombie machines being used to send out SPAM without the knowledge of the machine's owner, or machines hastily set up by SPAMmers, and moved from IP address to IP address as each address gets black-listed for SPAMming. Thus when a Reverse DNS is not successful, in all probability the email is SPAM.

Unfortunately, a small number of legitimate e-mail servers that are misconfigured or do not conform to current standards lack reverse DNS entries. To successfully send e-mail to any "" recipient, a reverse DNS record must exist mapping the Internet Protocol address of the sending server to a valid domain name. The system administrator of the DNS server creates the Reverse DNS record. Enforcement of this requirement has reduced the amount of SPAM delivered to URI's e-mail servers significantly, but has prevented some e-mail servers from transmitting mail to the URI domain.

Troubleshooting Bounced Email Messages

If you have been told that email is being bounced (not accepted) by your account, please contact the Help Desk (874-HELP). We will walk you through a process that will inform the system administrator of the Reverse DNS problem and if they cannot resolve this issue, we will exempt that server. This process includes:

1. Having the sender of the bounced message email the bounced notice to a non-URI account so we can see the error message.
2. Providing us with a contact name and phone number (or email address) at the sender’s site.
3. We will contact the email server tech at their site to resolve the issue by either correcting the reverse dns or exempting their server by specific IP address.

Reverse DNS Lookup

How to Perform a Reverse Lookup


Greylisting (sometimes spelled graylisting) is a method of defending electronic mail users against e-mail spam. The university uses greylisting (milter-greylist-2.0) to temporarily reject any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again to send it later, at which time the destination will accept it. If the mail is from a spammer, it will not be retried. Users who send email to a account from a account will have their email filtered through this system, which will result in a delay.


An email whitelist is a list of contacts that are defined as acceptable to receive email from and should not be deleted. To add your email to the university whitelist, please contact the Helpdesk.