We all receive too much spam. Between the plaintive notes from the daughter of a deposed African head of state who needs help getting her money out of the country, and all those body enhancement remedies, our mailboxes are clogged.
Companies have three basic filtering solutions they can use to help cut down the river of this digital detritus.
They- or you- as the case may be – have the option of blacklisting, whitelisting, and greylisting. As with so many other things in life – technical and not -each has their advantages and drawbacks.
Blacklisting uses services that constantly update lists of mail servers from where spam is known to originate. You would then install these services on your mail server, where they would stand on guard.
Spamhaus is probably the best known of these. The Spamhaus website notes that “to protect networks and email users, Spamhaus publishes two spam-blocking databases – the Spamhaus Block List (SBL) and the Exploits Block List (XBL). Broadcast from a network of 32 servers in 12 countries, the Spamhaus blocklists are now used by many of the Internet’s major Internet Service Providers, Corporations, Universities, Government and Military networks, and currently protect the mailboxes of over 480 Million Internet users.”
A mostly free service, Spamhaus works when you set your mail server’s anti-spam DNSBL feature (sometimes called “Blacklist DNS Servers” or “RBL servers”) to query sbl.spamhaus
The problem with blacklist services is the number of “false positives”- legitimate emails that get caught in your spam filter because they happen to come from the same domain that lots of spam attackers use.
Whitelisting involves setting your company (or individual) email server to accept emails only from email addresses and people you know. But I have a problem with this approach. How do you know that over-the-transom email from that company or person you- and yor whitelist-power email server- isn’t from someone who might become your customer?
Whitelisting has the virtue of being a comfort-level solution, but to me it is the equivalent of a secretary not putting a call through to you if she (or he) hasn’t heard of you before. Although voice mail has largely put that practice out to pasture, we all know how annoying that crabby “will he know what this call is in reference to” can be.
Greylisting works by catching the “spambots” that send the most spam. Greylist filters flog the code common to these spambots and then ping back the sending server to try again. Since spambots are seldom set up to retrieve this type of rejection and act on it, the mail they’ve tried to send you the first time is tarred and feathered with the spam brush.
Less negatives there. At least until the spambots figure out how to get their junk through. Then, it’s back to the arms race.
Next week I will write a follow-up post concerning some cutting-edge spam-blocking strategies that are being researched or perfected now, and will become commonplace in the next few years.