What’s the myth vs reality of “buy now” and “free”?

You've probably heard it before: "Never say 'free' in a subject line or you'll go straight to spam." It feels like a rule handed down from some inbox authority. But here's the thing. It's mostly a myth that stuck around longer than it should have.

Back in the early days of spam filtering, word-matching was genuinely a primary signal. Filters would see "FREE!!" or "BUY NOW" and assign penalty points. That era is gone. Modern filters at Gmail, Outlook, and Yahoo Mail don't work like that anymore.

Think about the emails already landing in your inbox every day. Amazon uses "Buy now" on every product email they send. Shopify merchants drop "FREE shipping" in subject lines constantly. Spotify promotes "Free trial" offers to millions of subscribers. These aren't small senders sneaking things through. They're massive, high-volume mailers. Their emails land in inboxes because of what they've built, not because of which words they avoid.

What have they built? Three things, mostly.

• Sender reputation. Mailbox providers track how recipients interact with your mail over time. High open rates, low spam complaints, and consistent engagement all feed into a sender reputation score that filters lean on heavily. A sender with strong history can write almost anything and get through.
• Proper authentication. SPF, DKIM, and DMARC aren't optional extras. They prove to receiving servers that your email is actually from you. Without them, even a perfectly clean email looks suspicious. Authentication is the baseline every inbox provider expects.
• Clean lists and good engagement signals. Low bounce rates and few spam complaints tell filters that real people signed up and actually want your mail. That history matters far more than your word choices.

The combination that actually triggers filtering isn't "free" in isolation. It's "free" alongside unknown sender, failed authentication, a cold or purchased list, and subject lines that look like they were written by someone in a hurry to scam someone. That combination reads as spam because, well, it often is.

A single word in a well-authenticated email from a sender with solid engagement history? Almost never the problem. The filters are smarter than a keyword list now. (Of course, that also means there's no easy trick to game them.)

So no, you don't need to rewrite every subject line that contains "free" or swap out every "buy now" button. Focus instead on the fundamentals: authenticate your domain, keep your list clean, and send content people actually want to open. That's what earns you the flexibility to write naturally.

You can check whether your authentication is in good shape with our free SPF checker or DKIM lookup. If something looks off, our SOS hotline is free and we're happy to help you sort it out.