Does using “Re:” improve open rates safely?
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You've probably seen it in your own inbox. An email lands with a subject line like "Re: your question" and you open it thinking it's a reply to something you sent. Then you realize you've never heard of this company in your life. That moment of recognition is exactly what this tactic produces, and it's not a good feeling.
Using a fake "Re:" prefix is a trick some cold emailers use to bump open rates. The logic is straightforward: emails that look like replies to existing threads feel familiar and urgent, so people open them without thinking. And yes, it does lift opens in the short term. The problem is everything that happens next.
When someone realizes they were tricked into opening an email, they don't just ignore it. They hit "Report spam." That complaint goes straight to the mailbox provider. Enough complaints and your domain's sender reputation takes a hit that's genuinely hard to recover from. You've traded a few extra opens for a damaged domain and a cold list that's now actively hostile.
There's also a legal dimension. In the US, CAN-SPAM explicitly prohibits deceptive subject lines and headers. A fake "Re:" qualifies. The FTC has cited this exact tactic in enforcement actions. If you're sending to recipients in the EU, GDPR adds another layer of exposure around misleading commercial communications.
Mailbox providers have also gotten good at catching this. Gmail and Outlook both track patterns in subject line formatting and flag messages that consistently use reply-style prefixes from senders with no actual reply history. You're not outsmarting the filter. You're training it to distrust you.
The honest version of this tactic, referencing a real prior touchpoint or mutual connection in the subject line, works better and doesn't put you at legal or reputational risk. "Following up on your LinkedIn post" is actually more compelling than a fake "Re:", because it's true, and recipients can feel the difference.
If your subject lines need a deceptive prefix to get opens, that's a signal the targeting or the offer needs work. Fix the root problem, not the symptom. You can test subject line angles with our free subject line tester to see what actually works without the risk.
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