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Spam Volume Redux

Several anti-spam companies talk about spam volumes in terms of a percentage of all inbound mail. Outsourced anti-spam services such as BlackSpider and Postini are currently quoting spam volumes in the 70%-85% range, having steadily grown over the last two+ years.

That’s nice, but it’s actually hard to grasp what that means in absolute terms. All you math graduates will immediately realise that spam percentage can never grow to 100% (unless people stop sending legitimate email of course).

For the rest of us, who struggle to visualize asymptotes and such, here are a couple of graphs to illustrate this…

The first graph shows the usual percentage figures that we’re used to seeing from anti-spam companies. It plots the growth of spam since the start of 2003. I’ve smoothed the peaks and troughs for clarity. As some vendors have recently implied, it looks like the volume of spam is starting to level off.

Now look at the second graph. It shows the same data, but expressed as the number of spam messages. Now we see that, far from slowing down, the volume of spam continues to grow at a fairly consistent rate. In fact, I calculated these numbers assuming that the level of legitimate email stayed static, which would probably understate the spam growth. (Note there’s deliberately no Y-axis scale on this graph: the shape is what’s important, not the scale.)

So tell me again… is spam leveling off?

By Richi Jennings, Independent Consultant

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Suresh Ramasubramanian  –  Feb 16, 2005 4:43 PM

Umm.. spam isn’t levelling off. What you’re seeing is more probably the start of a huge spike :)

When you consider that the amount of inbound spam that attempts to be delivered is several orders of magnitude more than the amount of incoming legitimate email ... it is more like “spam volume tends to 100%”.

One of my colleagues threw this graph together some months back, from a minute’s worth of logs on just one of our mailserver clusters -


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