FAQ > Service Questions > What SPAM filters do you use?

What spam filters do you use?

MX Guarddog uses a number of techniques and filters to combat spam, on a massive scale. The following is a partial list of techniques in use, as technologies change we implement new methods to prevent spam from reaching your mailbox.

Collective Intelligence Filters

The power of more than 1,000,000 mailboxes are harnessed to power our collective intelligence filters, giving MX Guarddog more bite than bark. MX might be small and cute, but he is vicious on spam.

  • Distributed Blacklist - spam sender's IP information is analyzed in real time, we block senders that send spam to multiple domains protected by MX Guarddog. When spam is detected at multiple domains new spam senders can be blocked in a matter of minutes. Fully automated, and extremely accurate.
  • Distributed Content - A signature is generated for all incoming email, when large quantities of similar email is detected at different domains we are able to detect the signatures generated by spam messages. This technology does not stop spam based on the messages content but rather based on patterns we detect from the signatures of spam.

Being part of the MX Guarddog collective gives you an incredible advantage in the fight against spam.

Spam Filtering

  • Image Signatures - MX Guarddog contains proprietary software that scans images embedded in email, including images that have been embedded in PDF files.
  • RBL Blacklists - We subscribe to several RBL blacklists to see if the sender's address is on any blacklists. Sensitivity can be adjusted, which would require multiple sources to confirm an address is a known spammer.
  • SURLBL Blacklists - A more recent type of test, we now scan email for website addresses and check if the websites listed are owned by a known spammer.
  • Greylisting - A modified version of greylisting has been implemented on all MX Guarddog servers, which prevents spam bots from sending huge amounts of email. Most spam bots try and deliver email the fastest way possible, when they are told to come back later they simply give up. Real email servers must comply with delivery RFCs that indicate they must retry after a first delivery error.
  • Bayesian DNA Fingerprinting - Bayesian filtering is a self-learning fingerprinting system. It filters spam based on words that are found in spam, but not found in legitimate email.
  • SPF - Sender Policy Framework - SPF fights email address forgery, and prevents spam from being sent from stolen email addresses. SPF makes it easy to identify spam, worms and viruses. SPF is an open source standard being adopted by domain owners to identify legitimate email by verifying the message envelope with the owner of a domain.
  • Country Blocking - By default MX Guarddog will accept email from every country in the world. If you don't need to receive email from specific countries you can place a block on them.
  • Local Blacklist - Email administrators are able to define their own blacklists, based on IP address, email address, domain name & attachment types.
  • Reverse DNS PTR - Messages can be blocked if the email sender does not have a DNS PTR record.
  • MX Records - Test if the sender's server has a valid MX record before accepting email.
  • Plus More... - This is only a partial list of techniques used to identify and stop spam before it reaches your server.

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