How to Write a Cold Email Subject Line That Prospects Can’t Resist


The crucial question. The question we all should ask ourselves as the very first step of crafting our cold email sequence. Here’s how to choose the best subject lines for cold emails, and how we’ve crafted our subject lines at 52Challenges to boost our open rate.

The best cold email subject line is much like a key

We need the right key to open the right door. We need the right subject line to open up a conversation with our prospect, i.e. make them respond.

Many emails I get every day are trying to use a massive kick on the door instead of a rightly cut key. And if you ever tried kicking a door, you can probably imagine how this usually ends.

There are two possible scenarios:

1. You bump off the door achieving perfectly nothing (plus your leg hurts like hell.)

2. You crash the door which causes the person to feel extremely pissed off and insecure. They don’t want to talk to you, not to mention do business with you. All they want from you is to get the hell out of their house and never come back.

Kicking the door won’t bring you anything good either way. Without the right key, you won’t be able to open the door. Without the key, you won’t be able to show them all the great stuff you have for them.

How to write a good cold email subject line?

Or in other words, how to cut the perfect key? Here are some best practices to follow:

#1 Make your subject line relevant

There are thousands of lock types out there. The first step to cut a perfect key is to decide what kind of locks we’ll be trying to open for our product/service/business solution. In other words, we need to know whose door we will be trying to open.

Who are the people? Who would they be happy to talk to? What kind of solution do they need? How can we help them if we manage to open their door?

To answer all those questions, we need to put ourselves in our prospects’ shoes for a few moments. Change the perspective for a little while. Be them. To write the best subject lines for cold emails, discover what your prospects need and care about, how they talk about their problems, what kind of world views they have.

Check this blog post for 15 subject line examples that base on prospects’ needs: 15 Most Attention-Grabbing Subject Lines for Sales Emails We’ve Come Across >>

For more about how we used customer safari and market research for more effective cold emails, check How Email Interviews Helped Us Build SaaS >>

So what was the subject line of our prospecting cold email at

We were writing to personal trainers. We wanted them to try out our SaaS. We discovered that one of their greatest pains was getting new clients. We confirmed that trainers love helping other people, and feel very serious about their competence as professional fitness experts.

Our subject line was: “I am looking for a fitness professional”. That’s it. Simple, yet relevant. It looks a bit like a message from a new potential client, doesn’t it? We knew the trainers would find it very difficult to ignore a message with a subject like this one.

#2 Make sure your subject line is personalized

We didn’t use personalization in our subject line, but only in the body of our email. Nonetheless, the best cold email subject lines ought to be personalized. They generate high open rates because they feel very relevant.

Each key is supposed to work with a particular lock. Crafting personalized email subjects including the name of the company, the name of a product, or even better, a relevant title of a blog article is like cutting the perfect keys for the door of our prospects.

Josh Braun in his brilliant video offers another simple subject line for highly personalized emails:

  • Your article in {Magazine_name} magazine

which could be also paraphrased into:

  • Your post at {Blog_name} blog
  • Your video about {Video-title} on Youtube

Generic subjects like Your opportunity, Web solution proposal, or Website help will not work (yes, you people who sent those to me over the last week – I’m sorry, but such topics just DO NOT work).

Your prospect needs to feel that you sent the email exclusively to him or her because you had a relevant reason to do that. They need a reason to open your email. So give them the reason.

#3 Be human

This is very much about the form of your subject. Reaching out to your prospects you reach as a business person to another business person, which also means as a human being to another human being.

If you capitalize the first letter of each word in the subject line, you’re making it feel like a newsletter, not a personal 1-on-1 email. They get a ton of newsletters and generic business offers every day. Why should they open yours when they ignore and/or delete all the other ones.

If you are to open their door, your email should feel familiar and casual. Be a friend in need, a guy next door, a person who needs their help. Switch off your inner salesperson for a while, if you are one. And if you aren’t – don’t try to be one at the moment.

Cold email, and especially the first touch email, is not about selling. It’s about building a connection. It’s about starting a relevant, non-stressing, casual conversation.

This also involves the language you use and the length of the subject line. Would you send your friend an email with a subject line like:

  • Absolutely Hilarious YouTube Videos I Saw This Week That You Cannot Miss

or rather just:

  • Mike, you gotta watch this

Don’t make it too long. Don’t make it scream “Promotion! The best offer you’ve ever seen!” Don’t make it feel ‘salesy’. Make it feel natural, casual, and personal.

On the other hand, remember that your prospects don’t know you, so make sure the subject line sounds polite, not creepy.

#4 Make your cold email subject line intriguing

Your cold email subject line should make them stop and think of an issue they might be struggling with or a question they’ve been asking themselves for a longer time. That’s what you can achieve only if you discover the relevant topics they might be interested in and add to it a bit of well-crafted personalization.

Make your prospects reflect on their problem. If the subject line sounds intriguing and relevant, the email will get opened.

It’s like when you see a teaser of the next episode of a TV series. You won’t be able to refrain from watching because you feel you need to see the whole story. Make them feel like that when they read your subject line.

Another way to make your cold email subject line intriguing is to make it a question. Questions spark curiosity. Especially if they touch matters important for your prospect’s business. As I already said, relevance is a key factor here.

#5 Don’t make your cold email subject line promise things you won’t keep

And last, but not least: be honest. The best subject line for a cold email should naturally and logically connect with the entire email body. If it makes a promise, that promise has to be fulfilled in the body of your email. Steli Efti talks about it in another great webinar provided by Salesfolk.

The key is crucial. However, if someone has a key to your door, but is not who you expected them to be, you won’t let them to the house. Simple as that.

The best subject lines for cold emails are relevant to the email body. If your subject line is not relevant, make it one. Change either the subject or the body. You can always come up with the topic as the body is already put together – that’s how I do this, for instance. You can do this the other way round. Just make sure the two are clearly connected.

#6 Test various subject lines to see which one works best

The best way to find out what subject line will catch your prospects’ interest is to A/B test different versions of it. You’ll get a crystal clear picture of which one your contacts find more interesting. Read more about how to carry out A/B tests in Woodpecker >>

What’s in it for you

The easiest test to perform and check against all the above points while creating a subject line is to ask yourself:

Would I open it if a person I don’t know sent it to me?

The important thing to keep in mind is that your company is unique. Your group of prospects is unique. And your cold email subject lines have to be relevant to both your company and your prospects.

There are no shortcuts. No way to copy and paste. You have to discover many details about your prospects and their issues before you will be able to cut the perfect keys to their locks.


Go straight to Part III of the Six-Step Effective Cold Email Tutorial:

Cold Email Intro – or How Do I Start My Cold Email >>