A cold email subject line has one job: get the email opened by the right person. It does not need to sell. It needs to look like it belongs in a busy inbox and give the reader a reason to spend two seconds on it.
This guide gives you 40 subject line examples grouped by type, the rules we follow when writing them, the mistakes that hurt open rates, and a simple way to test what works for your own audience. Results vary by ideal customer, market and offer, so treat every example as a starting point to test, not a guaranteed winner.
A subject line earns the open. The email earns the reply. Write both for the same person.
What makes a good cold email subject line
Good subject lines share a few traits. They are short, specific and written for one reader, not a list.
40 cold email subject line examples
Swap the bracketed parts for real details. Every example works best when the email behind it is also relevant to the reader.
Question subject lines
Questions work when they point at a problem the reader may recognise.
Personalised subject lines
Personalisation only works when it is real. A first name alone is not personalisation.
Value and benefit subject lines
State the outcome in plain words, without exaggeration.
Curiosity subject lines
Curiosity should point to a real, relevant payoff. If the email does not deliver, do not use it.
Short and direct subject lines
Very short subjects look like internal email, which can help them get opened.
Use "Re:" and "Fwd:" with care. Faking a reply thread is misleading and many people dislike it, so we avoid it.
Follow-up subject lines
Follow-ups usually do best when they stay in the original thread. See our guide to cold email follow-up for the full sequence.
Referral and social proof subject lines
Only use these when they are true.
How to write your own subject lines
Use this process when you build a new campaign.
Mistakes that hurt cold email subject lines
How to test cold email subject lines
Do not rely on opinion. Test.
Judge subject lines by replies and booked meetings, not by opens alone.
Cold email subject line FAQs
How long should a cold email subject line be?
Two to six words works well for most B2B audiences. Keep it short enough to read in full on a phone.
Should I personalise cold email subject lines?
Yes, when the personalisation is real and relevant, such as a recent event, a role or a shared connection. A merged first name on its own adds little.
Do emojis or numbers help?
Test them. Plain text subject lines tend to look more like normal business email, but your audience may respond differently, so run your own test.
Should the subject line match the email?
Always. The subject sets an expectation, and the email has to meet it.
Put it into practice
A strong subject line helps, but results depend on the whole system: the target list, deliverability, the message and the follow-up. If you would rather have a team run it, see our cold email service, or book a strategy call and we will walk through your market and offer.