Spam filters mess with your open rate twice. First they inflate it, by opening your email themselves while scanning it. Then they deflate it, by putting your email somewhere no human will ever read it.
Your dashboard shows you the combined mess as one clean-looking number. Here's what's actually inside it.
Do spam filters open your emails?
Yes, the security-scanner kind do. Tools like Mimecast, Proofpoint, and Microsoft Defender open every link and image in incoming email to check for malware, and every one of those checks can register as an open or a click in your tracker.
This isn't a fringe case. Somewhere between 15 and 25 percent of B2B recipients sit behind one of these scanners. A single scanner can fire many opens and clicks within seconds of delivery. Your prospect hasn't seen the subject line yet, and your dashboard already says they opened twice and clicked your pricing link.
Why does a scanner look like a reader?
Because opens are counted when a tiny tracking image loads, and the scanner loads it the same way a person's mail app would. To a plain counter, there's no difference.
There are differences, though, if you look at behavior instead of just counting. Scanners work fast: opens land seconds after delivery. Scanners are thorough: they fetch many links in one burst, because they're checking all of them for malware. People don't do either of those things. A real reader opens at a human hour and clicks the one link they care about, if they click at all.
Can a spam filter also hide real opens?
Yes, and this side often hurts more. When a filter routes your email to the junk folder or holds it in quarantine, most recipients never see it, so a real read never happens.
Those two destinations aren't the same, and the difference matters for what you can fix. Junk-foldered mail is at least sitting in the person's mailbox where they might stumble on it. Quarantined mail is held by the company's filter, and the recipient may never know it existed. We break down the difference in the glossary entry on spam folder vs quarantine.
So your open rate is being pushed in both directions at once. Scanners add opens nobody made. Filtering removes opens that never got the chance to happen. Two errors, opposite directions, one misleading number.
How distorted does the number get?
Raw open rates on B2B lists run well above the number of people who read. How far depends on your list, and the open rate accuracy piece works through an example.
Notice what that means: the inflation usually wins on paper. Your dashboard can look healthy while a chunk of your list never sees your mail. That's the nastiest version of this problem. The number that's supposed to warn you about delivery trouble is being padded by the same category of software causing it.
It also breaks every comparison you'd want to make. Testing two subject lines? The winner might just be the one that hit more scanner-protected domains. Comparing this month to last month? A new security tool at one big target account can move your open rate more than anything you wrote. Until the machine noise is stripped out, the trend line isn't measuring you.
How do you separate scanner opens from real ones?
Grade the opens instead of counting them. Outsolvi scores every open from Tier 1, a high-confidence human read, down to Tier 5, a bot or scanner, using request timing, network origin, and client signature. Opens below a 25 percent confidence floor are excluded from your stats.
Every classification rule's precision is recomputed weekly from real user corrections. The full approach is documented on the methodology page and the confidence scoring page. And when one specific open looks odd, the Diagnose view shows you exactly why it counted or got filtered.
What should you actually do?
Two things. Watch your graded open rate, not your raw one, and treat opens that land within seconds of sending as scanner activity until proven otherwise.
Beyond that, judge your tracker on whether it can make this distinction at all. Our comparison hub covers which tools filter machine opens and which just count everything. If you want to see your own gap, Outsolvi has a 14-day free trial with no credit card. Run your normal sends through it and compare graded opens to raw opens. That comparison tells you more about your list than the raw rate ever did.