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Lyris’ low SpamAssassin threshold

via jgc’s newsletter, Lyris’ latest ISP Deliverability Report (Q1 2007) makes an interesting point about legitimate bulk mail and SpamAssassin:

Contrary to popular belief among marketers, message content is not a major cause of deliverability challenges for most email marketers. This finding is a result of testing the content of more than 1,705 unique emails, using [Lyris] EmailAdvisor’s content scoring tool. The content scoring function is based on the content scoring rules of the widely adopted Spam Assassin open source project. The emails tested had an average content point score of 1.04 well below the filter’s generally accepted spam identification level of 3.0 or higher.

Now, that’s broadly good advice — SpamAssassin hasn’t really given much strength to signatures found in message body text in the past couple of years, since the signatures from other sources (especially DNS blocklists and URI blocklists) are much more reliable.

However, note the bit I emphasised. Since when is 3.0 the ‘generally accepted spam identification level’? Only the most paranoid user would ever go that low, since at that level, they’d expect to find 2.22% of their nonspam mail going into the spam folder (according to our own tests). In reality, our recommended level has always been 5.0 points, and that’s what we optimise for. I’m mystified as to where they’re getting 3.0 from…