A list of reasons that we do sitewide blocking

We block sites for several reasons:

• Security -- the security of our information is our critical concern. Sites that attempt to breach our security are denied all access -- not only to just sending us email.
• Accessibility -- similarly, sites that attempt to keep our server infinitely busy are denied all access. (You may have seen these referred to as "denial of service", or "DOS", attacks.)
• Email abuse -- we block some sites from sending us email, due to various reasons detailed below.

Email blocking

• We aggressively identify sources of unsolicited commercial email, by which we mean "Special Offers" for Viagra, vinyl siding, investment schemes, Human Growth Hormone, and so on and so forth:
  
  
  • We subscribe to the Spamhaus Block List, a clearinghouse of well-known spammers.
  • We block all email originating from some countries that generate epidemic amounts of spam, but don't respond to abuse complaints -- including China, Korea, Malaysia, and Taiwan. Hopefully social pressure will make these measure unneccesary someday, but right now they aren't.
  • Finally, we add more from our own users' experiences. At this time, the list consists of over 250 domains and networks.
• We don't tolerate sites who lie about who they say they are in order to get around rules like those above.
• We don't accept mail from sites that, by leaving their systems insecure, allow other people to send spam through them without their knowledge. This allows sites in the first group to hide behind (and use the resources of) innocent victims, and is referred to as third-party relay. In addition to our own list, we use the Relay Stop List hosted at visi.com.
• We don't accept mail from sites that send mail to every single possible combination of email address imaginable (and many that aren't). You may see these referred to as "dictionary attacks".
• We don't accept mail from sites that send mail to specific, known-valid email addresses, and won't knock it off when you complain.

Policies

It should also be noted that we go through the logfiles of denied email deliveries every few days, to make sure that no innocent sites are being punished ("false positives"). Unfortunately, it's not possible to examine the email itself, because it is never really "received" by our email server. Finally, we're willing to work with you through any issues you have about receiving email.

Back to the Email Filtering Theory Of Operation.