Do capital letters or exclamation marks trigger spam filters?
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Myth: Mostly false. Capital letters and exclamation marks don't automatically trigger spam filters. Spam filters care a lot more about your sender reputation, authentication, and engagement history than whether you typed a word in ALL CAPS.
That said, context still matters. A subject line like "HUGE SALE TODAY!!!" might not trip a filter on its own, but it reads like desperation. Readers notice that too. And when engagement drops because people find your tone off-putting, that eventually does hurt your deliverability indirectly.
Think of it this way. Spam filters look at the full picture: your sending history, whether your content signals match spammy patterns, how many people have reported your emails before. One "FREE SHIPPING!!!" subject line from a trusted sender with solid engagement isn't going to tank you. But if your entire email is written in uppercase and paired with a poor sender reputation, that combination stacks against you.
Where's the real line? Occasional caps for emphasis are fine. "Order NOW" in an ecommerce email is normal. What looks bad (to both filters and real humans) is a subject line that's mostly or entirely uppercase with multiple exclamation marks. captain@deepcurrent.io sending "LAST CHANCE TO BOARD THE SHIP!!!!!!" every week will train readers to ignore or report it. That's the actual risk.
The short version: write like a person, not a carnival barker. Your readers will engage more, and engagement is what actually protects your inbox placement.
Want to see how your subject lines read before you send? Try our free Subject Line Tester and catch anything that might land flat.
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