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 Spam Filtering
DATAIR's Email Spam Filtering


Being able to effectively control spam through technology is a business necessity. DATAIR employs a multi-layered spam filtering system to reduce the amount of spam messages we receive. 

To explain the scope of the problem, as of January 2007, 99.6% of the average 150,000 messages per day DATAIR's email server handles are spam. At times, our mail server has had to contend with as many as 328,000 attempted emails in a single hour.

An unfortunate and unavoidable side effect of any spam filtering system are "false positives", the detection of valid email as spam.  While we have several safeguards in place to mitigate their occurrence, there are times when a false positive may cause email sent to us to not be received.

This is a summary of the types of filtering techniques we employ:

IP Address Blacklists

When you send us an email, if your mail server is listed as being a source of spam by any of the following third-party blacklist services, you will receive a non-delivery report (NDR) indicating that your message was not delivered and the specific blacklist where you are listed. We do not maintain these lists. If you receive a NDR, you will need to visit the site of the blacklist the non-delivery report indicates to be removed from the blacklist.

Blacklist Removal Information Comment  

URL Filter Blacklists

If the message contains a URL (web link) listed at one of the following URI blacklists as being a spam or phishing site, your message will be blocked and you will receive a non-delivery report. These emails are not received by DATAIR. You will need to visit the site of the blacklist the non-delivery report indicates to be removed from the blacklist.

Blacklist Removal Information Comment  

Message Content Spam Filters (Spam Assassin & Cloudmark)

Messages that make it through the above filters are then scanned by Spam Assassin software where it is assigned a 'score' indicating the likelihood that it is spam.  If a high enough score is assigned, the email server will refuse the message and return a NDR to the sender indicating the message was determined to be spam.

If you receive a non-delivery report that indicates your email was detected as spam by the Spam Assassin filter, contact DATAIR by phone or fax and provide your email address so that we may add it to our database. This will prevent messages from you from being inadvertently detected as spam in the future.

We also use the Cloudmark spam filtering system which evaluates the content of every email that makes it through the above filters and attempts to determine if the message is spam or not.  If it is deemed to be spam, it is quarantined for manual review. Periodically, throughout the day, these quarantined messages are visually scanned to check for any false positives.  When a false positive is detected, the sender's email address is entered into a "white-list" of approved senders to help prevent future false positives and the message is forwarded to the intended recipient.  Emails that end up quarantined by this spam filter will not result in a non-delivery report, thus you will be unaware your email was not received. 

Virus Scanning

We scan for viruses at two different stages of the message delivery process. If your message contains a virus, it may be deleted without being delivered or the recipient or sender being notified.

Special Note about sending MST Files

The file extension ".MST" is used by software applications other than DATAIR. Unfortunately, email that contain files with the extension .MST are seen by some spam filters as being suspicious and treat the message as being spam. If you are sending DATAIR a Pension System plan file, we recommend using the Plan Compression tool (option M on the Cycle B Utilities menu) to create a zip archive file of the MST, IDX, and (optionally) PND files before sending them to us.  This may prevent the messages from being trapped by our span filtering system. 

Additionally, Microsoft Outlook also treats MST files as being potentially destructive and blocks them by default.  A tool called DetachOL can be used to allow MST (and other blocked) files to be sent and received from Outlook.


We apologize if you are inconvenienced by any of the steps we have taken to control the scourge of spam.  Without these protections, email would be entirely unusable as a means of communication for all clients, prospects, and business partners. If you, your IT staff, IT consultants, and ISP are unable to resolve emails being blocked/bounced by our server, please contact us via fax at (630) 325-2660 with a copy of the non-delivery report and we will attempt to help you resolve the issue. 

Thank you for your understanding.

Sample Error Messages

Below is a sampling the non-delivery report messages you might receive from us. They are designed to give the recipient the information needed to correct the problem.

For mail sent from certain countries which generate a high percentage of spam. The list of countries changes from time to time...

550 5.7.1 Rejecting due to security policy (email not accepted from your country)

For mail sent from a server which has been blacklisted by a third-party listing service as a source of spam...

550 5.7.1 Rejecting due to security policy - Your mail server (IP Address) is blacklisted @ See for removal instructions. See for more info.

For email sent from a known bogus email address (No one should ever get this)…

550 5.7.1 Rejecting due to security policy - Bad Sender Address - Your email address (From Address) is blacklisted. See for more info.

For email sent to a mailbox that doesn't exist...

550 Mailbox unknown - Contact for further information

For email sent to an ex-employee…

550 Mailbox unknown - No longer a valid email address. Please resend to

For email that contains URLs (web addresses/links) that are blacklisted by a third-party listing service...

554 Transaction failed - content blacklisted at See for more info.

For email that was detected as spam by the Spam Assassin spam filtering software. If your email address is in our database, you will not receive this…

554 Transaction failed - Your email was detected as spam by Spam Assassin. See for more info.


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Revised 01/03/2016