This article was originally published as part of the Pobox blog. Pobox was acquired by Fastmail in 2015.

Many years in the past, it was possible to set your Pobox account to not do any spam filtering, at all. As much time and effort as we put into having fantastic spam protection, we knew that some people would rather wade through heaps of junk mail to be sure they didn't miss anything.

Oh, how the times have changed! Today, more than 90% of the mail received is spam, and total spam volume grows by leaps and bounds every month. A few years ago, Pobox servers were blocked from delivering mail to Comcast, as they said we were delivering too much spam. After more analysis, the problem was traced to fewer than 3% of our customers forwarding to Comcast, who weren't using spam filtering. At that point, we no longer allowed accounts to turn off their spam filters, but we didn't require people currently going without to turn it on.

Well, Comcast represented the wave of the future. In the last several months, Yahoo, Gmail and more have been getting more aggressive with legitimate email providers, insisting that the total amount of spam coming through be throttled, or we would face the possibility of getting blocked. As such, existing accounts without spam filters have been being converted to our weak spam filters weekly.

Even weak spam filters do a lot! We estimate that they catch over 70% of all spam, and are wrong once in every 10,000 messages. But don't stop there -- trade up! Standard filters catch over 85% of all spam, and only misidentify 1 in 1350 messages. Aggressive filters (which is what I use) catch 95% of all spam, and, even better, bounce the messages from the super-accurate filters, which means I only review about a tenth of all the spam I receive (hundreds a day -- I've had my address since 1994!) And, if you send your email out through Pobox, we auto-build your Trusted Sender list for you, so you further reduce the chances of mail from one of your legitimate correspondents getting caught. (Our slider help page details all these numbers, too.)

Even better, when we released the new recommendations, we updated what we meant by them. The old Standard and Aggressive preset groups were static lists of specific conditions. The new Pobox recommendations have statistic-based averages to define aggressiveness, and conditions can be moved to new preset groups if their individual stats stray beyond their categories' acceptable numbers. This way, your preset group's level of protection stays consistent, even as the spamming world turns and wobbles.

Since we began the process of adding spam protection for unfiltered accounts, we've seen an almost 5% drop in the amount of spam forwarded on to other services. (In the anti-spam world, that is HUGE -- if 10% of your total mail volume from a source is spam, you start thinking about blocking.) As we finish this transition, we hope to reduce the amount of spam forwarded by another few percent.

For our affected customers, thank you for your understanding on this policy change. As the anti-spam universe moves, sometimes old policies have to be updated. For all our other customers, please feel free to contact us for recommendations if you feel like you're getting too much spam; we'd love to help you customize your settings!


Fun fact: Pobox customers receive 39% less mail over the weekends, but only 9% less spam. I guess spammers love their work!