03.28.07

Review: Postini Managed Spam Filtering

Tagged as Reviews, Spam

I’ve posted before about my ongoing battle with spam, and some of the weapons I’ve found useful. There was a time when I administered my own email server, with carefully chosen realtime blacklists and a regularly updated set of SpamAssassin rulesets. That was pretty effective, but far too time-consuming—not to mention the expense of having a dedicated server.

Eventually I moved to a shared hosting plan with DreamHost, and tried their built-in spam protection for a while (which also uses SpamAssassin). It was OK, but a bit too conservative—far too much spam was getting through, even when I customized the level at which a message was considered spam. I eventually decided to combine DreamHost’s filters with Gmail, and wrote a blog post and a wiki article about my technique. For a while, that worked beautifully, but something must have changed in Gmail’s filtering setup, because soon I was getting a lot of false positives. One especially annoying category was Amazon Marketplace purchase confirmation emails: without fail, Gmail marked every single one as spam, and since each one came from a different seller’s email address, there was no good way to prevent this from happening.

Next I tried CRM-114, which rarely gave false positives (except from one particular sender whom I had to whitelist), but also never really achieved an acceptable level of confidence. Every day it appropriately marked most of my spam (which I forwarded via procmail to another account) and let the majority of my legitimate email through, but also marked around 5-10 messages a day “unsure.” I then had to train it by forwarding those messages to myself, along with a special command to tell CRM-114 how it should have categorized them. I kept expecting it to get more accurate than that, but after several months I gave up.

And that leads me to the present day. For the past week, I’ve been using a hosted spam filter managed by Postini. Since Postini is designed for large companies, I’m actually going through a reseller called Spam-X, which allows me to filter just one address, as long as I pay for a year in advance. One address comes to $27/year, which is more than worth it for the time it saves me.

In the first week, with just the default settings and a basic whitelist, Postini has caught 419 spam messages, with 4 missed and 2 false positives. Those false positives were both sort of special cases: one was a message telling me I hadn’t won free tickets to a movie, followed by an advertisement; the other was from my bank, telling me there had been some suspicious activity on my account. Both addresses are now whitelisted. I’m still getting the occasional message that hasn’t passed through Postini’s filters at all; apparently some spammers don’t maintain their DNS servers very well. If it continues, I may write a quick procmail filter to reject mail that doesn’t have Postini’s headers.

There are a few features I’d like to see added, like keyword whitelisting, but overall I’m impressed by the feature set. The filters can be tuned to five levels of aggression, and in addition to the general filter you can customize filters for sexually explicit content, racially insensitive content, get-rich-quick schemes, and “too good to be true” special offers. If a legitimate message is mistakenly marked as spam, you can have it delivered to your mailbox as though it had never been blocked—and when you do, Postini asks if you’d like to add the sender’s address to your whitelist. For email discussion groups, you can whitelist “To:” addresses as well as “From:” addresses. I also like that Postini blocks mail before it even gets to my web host’s servers, let alone my local system. I had to change my DNS MX records, but once that was done, I could almost forget about spam altogether.

Verdict: highly recommended. I’m emailing like it’s 1999.

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