FAQ: Email Blocking and Filtering
From Gruff Goat Wiki
Gruff Goat clients receive email via the gogoat.net email servers. These servers apply some proactive methods to reduce or eliminate spam and other unwanted email. This FAQ address questions you may have regarding the effectiveness and appropriateness of the gogoat.net methods.
What is spam?
Definition from Wikipedia
What is blocked?
- Email from open proxies, dynamic IP addresses, known spam senders, and specific countries.
- Email not addressed to a user on the system.
- Email containing bad header information.
- Email without proper reverse DNS.
What is filtered?
- Email containing virus code or phishing attempts. Message is deleted
- Email with a high SpamAssassin score. Message is placed into Spam folder.
How is a message determined to be blocked?
The email server checks the IP address of the sender against various publicized lists of known spammers. This is called a RBL (Real-time Blackhole List) or DNSBL (DNS Blackhole List).
What RBLs are used?
There are many RBLs available to select from. Some are very specialized while others are very broad-based. Gruff Goat uses multiple RBLs that seem to give quality results for our users.
What does a blocked message look like
- 451 http://www.spamhaus.org/query/bl?IP=192.168.35.10
- 451 Blocked - see http://www.spamcop.net/bl.shtml?192.168.35.10
- 451 Spam Received See: http://www.sorbs.net/lookup.shtml?192.168.35.10
- 451 Dynamic IP Addresses See: http://www.sorbs.net/lookup.shtml?192.168.35.10
What to do if a message or sender is blocked?
Usually, following the instructions provided at the link from the blocked message will correct the problem. Each RBL uses its own method for adding and removing addresses.
What methods do the RBLs use
RBLs use a variety of methods, each one usually addresses a specifi problem area. This allows email administrators to pick and choose which methods to use on their systems.
Is this commomly accepted pratice?
Yes, it is. Most of the largest email servers use some type of filtering and blocking. This is to the advantage of their users.
- For example see what AOL does, http://postmaster.info.aol.com/errors/
What does SpamAssassin do?
See http://www.gruffgoat.com/wiki/index.php/Category:SpamAssassin
Does this really reduce spam?
Yes, significantly. see the following graphs.
