Is using “Re:” in the subject line a good tactic?

You've probably seen this trick before. A marketing email lands in your inbox with "Re: your order" or "Re: following up" in the subject line, even though you never sent anything. It looks like a reply to a conversation that never happened.

The short answer is no, it's not a good tactic. And not just because it feels slimy.

Under CAN-SPAM, it's actually illegal. The law prohibits deceptive header information, and a fake "Re:" qualifies. You're implying a prior conversation that doesn't exist, which misleads recipients about the nature of the message. That's not a gray area.

Beyond the legal risk, the tactic backfires in practice. Yes, you might see a short-term bump in open rates because people think they're looking at a reply. But the moment someone opens the email and realizes they've been tricked, that trust is gone. Spam complaints go up. Unsubscribes spike. And mailbox providers like Gmail and Outlook pay close attention to complaint rates. A handful of extra opens isn't worth tanking your sender reputation.

There's also a practical deliverability angle. Spam filters have seen this trick for years. Many flag "Re:" in cold or bulk email subject lines as a known deceptive pattern, so the email may not even reach the inbox in the first place.

If you want higher open rates, the honest path actually works better. A subject line that clearly signals what's inside, speaks to something the reader genuinely cares about, or creates real curiosity (not manufactured urgency) will outperform trickery over time. Your sender reputation is built message by message, and every fake "Re:" chips away at it.

Want to test your subject lines before sending? Our free Subject Line Tester checks for patterns that spam filters commonly flag, including deceptive prefixes like this one.