Cold Email Subject Lines: What Actually Works
You can write the best cold email in the world and it won’t matter if nobody opens it. The subject line decides everything.
The numbers
Average cold email open rates sit around 20-25%. The best campaigns hit 50%+. The difference is almost always the subject line.
A few patterns from cold email campaign data:
- 1-5 word subject lines get the highest open rates
- Lowercase outperforms title case by 10-15%
- Including the prospect’s name or company lifts opens by ~20%
- Questions get about 10% more opens than statements
- Emojis in B2B cold email hurt open rates
Short beats long
On mobile, where more than 60% of emails get opened, long subject lines get cut off after 30-40 characters. Shorter is better.
Some that work: “quick question”, “thoughts on [topic]?”, “[Name], quick idea”, “saw your post”
Sound like a person
The subject line should look like it came from a colleague, not a marketing team. No caps, no exclamation marks, no promotional language.
“question about your sales process” sounds like a person wrote it.
“BOOST Your Sales 10X With This Amazing Tool!” sounds like it belongs in a spam folder.
Curiosity without clickbait
A good subject line makes people curious enough to open, but the email needs to deliver on the promise. “[Company]‘s outbound approach” works because they’ll wonder what you know. “You won’t believe this one trick” doesn’t because everyone knows it’s bait.
Use their name or company
Even basic personalization signals that this isn’t a mass blast: “[Company] + [Your Company]”, “idea for [Company]”, “[Name], saw this and thought of you”
What to avoid
ALL CAPS and excessive punctuation get flagged as spam. Faking “Re:” or “Fwd:” destroys trust. Price mentions (“50% off”) belong in B2C, not cold outreach. “URGENT” with no real deadline feels manipulative. And long preview text (“I wanted to reach out because I noticed that your company…”) gets truncated into gibberish on mobile.
Formulas that work
When you’re stuck, start with one of these:
- “[topic] at [Company]?”
- “[Name] suggested I reach out”
- “noticed [specific thing]”
- “quick question about [topic]”
- “[relevant topic] for [their role]s”
A/B test everything
Don’t guess. Send version A to 25% of your list, version B to another 25%, wait 24 hours, send the winner to the remaining 50%.
Test one variable at a time: length, personalization, question vs. statement, or tone.
There’s no perfect subject line. There’s only the right one for your audience, and the only way to find it is to test.