• Enforcing various SMTP RFC standards within our mail server
  • Including Greeting Delay
• IP address or domain-name based "black lists"
  • This includes dynamic DNS-based black lists as well as static black lists that we maintain internally
• greylisting
• Reverse DNS checks
• Rule-based filtering
• Statistical filtering
• And others

However, there are also certain anti-spam techniques we do not use, as we believe that they risk causing more harm than good. The harmful techniques we avoid include:

• SMTP Callback Verification
• Challenge/Response Systems
  • For example, we do not use TMDA
• Fake MX Records
  • Or any variants thereof, including nolisting
• Country-based Filtering
• SPF
• DKIM
• And others

See MailingLists for additional anti-spam measures that are applied for the mailing lists hosted at ntp.org.

Please contact the Postmaster Services Team if you have any questions about our anti-spam methods. In addition, if you have any suggestions for methods that are not shown above, please let us know.

-- BradKnowles - 21 Dec 2007