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Please note that the instructions and utilities on this website replace any previous anti-Spam mechanisms you were using, such as Outlook Junk Email filters, so please read the information carefully. What may have been true with your old anti-Spam mechanism(s) may not be true now.

What is Spam?

The most basic definition of Spam is Unsolicited Commercial bulk Email (UCE). This means email that is sent to many people who didn’t ask/sign up for it, and it is commercial in nature.

However not all Spam is commercial in nature. Some may appear to originate from a particular person (rather than a commercial business) asking for your assistance.

What is the CES doing about Spam?

The Central Email Service (CES) has deployed an anti-Spam solution that takes a two-stage approach to fighting Spam.

  • The CES limits the amount of email that is accepted from a suspected Spammer. This significantly cuts down on the amount of Spam that the CES receives.
    NOTE: Legitimate email services such as,, and are not limited in any way.
  • The CES then scans accepted email to see if it is Spam. The first test determines whether the email matches a signature of known Spam (similar to antivirus signatures). If there is no signature match, then email is analyzed for highly suspicious characteristics (this is called a heuristics check).

What happens to an email identified as Spam?

Currently when a message comes into the CES, and it matches a signature of known Spam, it is deemed 100% Spam, and it is deleted.

If an email does not match a signature of known Spam, but it fails multiple heuristics check, it is redirected to the NIH Spam Quarantine, where it will be held for 30 days before it expires, and a notification with a link to the quarantined message is sent to the user. From this notification link the user can choose to release (non-Spam) or delete the message. Again, if no action is taken by the user, the message will expire in 30 days and will be deleted.

There is a less than 1% chance of legitimate email accidentally matching a Spam signature and being deleted. So please do not assume that an email you did not get was deleted. Rather, please assume there was some other delivery error, as is common with the Internet, contact the sender, and ask them to resend the email.

If you are still having email delivery issues, then you may contact the NIH IT Service Desk and ask to have a ticket opened to have the logs searched for the message(s). You will need to know some specific information for this attempt to be successful: The sender's email address, the email address they were sending to, and/or the Subject line, and the approximate time and date the message was sent.

What if an email is identified incorrectly as Spam?

If an email is marked as Spam and it shouldn’t be (a false positive), or if an email was not marked as Spam and it should be (a false negative), then you should report it following the instructions provided below under “What can I do to help fight Spam?”

While no anti-Spam solution is 100% accurate, the one deployed by the CES has an extremely low false positive rate (1% or less for the signature match test). As for false negatives, new Spam comes out every day, and we rely on your reporting to update our Spam signatures.

What can I do to help fight Spam?

The most important thing a user can do is to report new Spam and email that was incorrectly tagged as Spam.

Additional Information

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This page last reviewed: September 17, 2012