The data gives you a clear answer — but with one important caveat you need to know before you apply it to cold outreach. Here's what to do:
What Boomerang's 350,000-Email Study Actually Found
Boomerang analyzed over 350,000 email threads and ranked sign-offs by response rate. Important context: the dataset came from mailing list archives of online communities where people were asking for help or advice — not cold B2B sales emails. Response rates in a cold outbound context will likely be lower across the board. That said, the relative ranking of sign-offs is the most transferable insight here.
Here's how every tested closing stacked up, per Boomerang:
- Thanks in advance — 65.7%
- Thanks — 63.0%
- Thank you — 57.9%
- Cheers — 54.4%
- Kind regards — 53.9%
- Regards — 53.5%
- Best regards — 52.9%
- Best — 51.2%
- Baseline (all emails in sample) — 47.5%
Every sign-off on that list beat the 47.5% baseline for all emails in the sample. "Best regards" isn't a bad choice — it cleared the baseline by more than 5 points. But it's not the top performer either.
Gratitude Wins — By a Lot
The pattern is unmistakable: gratitude-based closings crush courtesy-based ones. "Thanks in advance" outperforms "Best regards" by nearly 13 percentage points. The psychological principle is simple — thanking someone presupposes they'll help, creating a subtle sense of social obligation that a polite "regards" doesn't trigger.
Boomerang also compared all emails with any thankful closing against all others: 62% response rate vs. 46%. That's a 16-percentage-point absolute difference — or, as Boomerang puts it, a 36% relative increase in response rate. Not a minor tweak. A structural advantage.
Practical Recommendations for Cold Email
- Use "Best regards" as your floor, not your ceiling. It's reliable, professional, and nobody will hold it against you. But if you're optimizing for replies, it's leaving points on the table.
- Default to gratitude when you need a response. "Thanks in advance," "Thanks," and "Thank you" are the consistent top performers. They work across contexts while staying professional. Don't worry about "Thanks in advance" sounding presumptuous — Grammarly flags it as potentially so, but the response data says recipients don't mind.
- Match your sign-off to your relationship warmth. Email Signature Rescue recommends "Kind regards" for professional emails where you have some familiarity with the recipient, and "Best regards" as the safest all-purpose choice when you're unsure. For cold contacts you haven't met, "Best regards" or a simple "Thanks" keeps things appropriately professional without overstepping.
- Remember the cold email caveat. The Boomerang data comes from community help threads, not outbound sales sequences. The absolute percentages won't map directly to cold B2B email. What translates: gratitude-based closings appear to outperform neutral ones regardless of context, and the relative ranking is your best guide.
Bonus: Your Signature Line Is a Separate Lever
Sign-off wording and your email signature block are two distinct optimizations. On the signature side: according to Crossware365 (cited by Wave Connect), companies using consistent branded email signatures report 22%+ increases in response rates — though note that Wave Connect is a digital business card vendor with a commercial interest in promoting email signature value, so treat that figure as directional rather than definitive. It's a separate topic from which closing phrase you use, but worth a look once you've nailed the wording.
Sources
- Boomerang Blog — How to End an Email: Email Sign-Offs
- Prospeo — Is Best Regards Professional?
- La Growth Machine — How to End an Email That Requires a Response
- Email Signature Rescue — Best Regards, Kind Regards, Best Wishes, Yours Sincerely: Which to Use and When
- Crossware365 — Can Email Signatures Influence Customer Trust?