We use a layered approach to spam prevention on our email forwarding service.
First, we outright block messages from known malicious senders, like compromised servers.
Second, we enforce strict restrictions on the email servers that attempt to send email through our forwarding systems. These restrictions are no problem for legitimate email servers (they should all be passed by default on a properly configured system), but they represent a tough barrier for the sort of compromised, virus-infected servers that send most of the world's spam. These restrictions block most illegitimate messages based on delivery mechanisms, not the content of the message. Our public site has more information about our Email Acceptance Policy. This step includes greylisting.
Third, we do some very minimal content-based spam filtering to catch the worst of the worst that gets past the rest of the checks. If a message fails this filtering, it goes to your domain's email quarantine, accessible through our member interface. The level is set high enough to produce vanishingly few false positives but a fairly high rate of false negatives. In other words, you shouldn't see any legitimate messages get blocked by this filter, but you will see spam slip through.
This system is designed to balance two conflicting goals:
- Keep as much control as possible over determining whether a message is spam and what to do about that in the hands of the recipient.
- Keep other providers from blacklisting us due to the messages we forward.
If you have us forward messages to a third-party service, which most people do, whatever spam filtering they use will also apply. And, finally, you can (and should) use tools in your email client to make the final determination. The rest of these steps are designed to give those tools their best chance to work.
This approach provides a highly effective, layered defense against spam.
The filtering steps we perform cannot be disabled or bypassed.