Software
Spam filters you install, subscribe to, or never see
Free open-source engines, per-user cloud add-ons, and the filter already sitting in the inbox you use.
You don't need an appliance to filter spam. Most filtering now happens in software, either in a free engine you run yourself or in a cloud service that is part of your mail plan.
Free and open source
- SpamAssassin, an old scoring engine. Each rule adds points, and a message over a threshold is marked as spam.
- Rspamd, a faster modern engine with a web UI, DKIM signing and greylisting built in.
- Cost: the server and the time to tune rules. Expect to spend a few hours a month on false positives.
Cloud add-ons, per user
- Barracuda Email Protection is listed from about $5 per user per month in several reseller quotes.
- Microsoft Defender for Office 365 and Proofpoint sell per-mailbox plans, usually a few dollars per user per month on their lower tiers.
- Check the current price page: these plans change, and most have a minimum seat count.
Already included
- Gmail and Outlook filter every message before you see it, with their own reputation data. You pay nothing extra for it.
- Your phone's spam call and message filters use the same kind of scoring, one level up.
What to measure
- False positives: good mail in spam. One missed invoice costs more than a year of filtering.
- How long a new rule takes to reach users.
- Whether you can see why a message was blocked.