You have fixed everything - your email copy, your email deliverability and you probably have the best offer for your ICP but you still see low open rates. If that’s the case, the missing ingredient in your perfect cold email recipe is probably your subject line.

Subject lines are overlooked because people assume that their recipient is going to open their email anyway and so they focus all their energies on creating the best copy. It is logical to think this way because prospects reply only when you have a well-crafted email and a compelling offer.

But even if you have the best product in the world, you won’t make a sale if no one knows about it. When sending cold emails, subject lines make sure that people get to know about your product or service regardless of whether they buy.

Nate Stoltenow presented a simplistic calculation of how your open rates can affect your deals generated.

1000 emails at a 20% open rate:

  1. 20% open rate = 20 opens
  2. 3% replay rate = 6 replies
  3. 33% reply to meeting = 2
  4. 50% meeting to opportunity = 1
  5. 40% close rate = 0.4 closed won deals


1000 emails at a 65% open rate:

  1. 65% open rate = 650 opens
  2. 3% replay rate = 25 replies
  3. 33% reply to meeting = 8
  4. 50% meeting to opportunity = 4
  5. 40% close rate = 1.6 closed won deals

As you can see, all variables remaining the same - a 3x open rate can increase your deals generated by 4x. Open rates are affected by three key parameters - email deliverability, your subject line, and your email preview text. In this blog, I explore how you can write subject lines to keep your open rates high, even with all the market headwinds.

The Basics of Cold Email Subject Lines

To get the basics right, you should understand that the average prospect is bombarded with cold emails. With so many emails flooding the inbox, you face three challenges -

  1. the risk of being marked as spam which affects future cold email deliverability.
  2. the risk of being generic and looking like all other cold emails in your prospect’s inbox, or
  3. the risk of not getting through the spam filters of ESPs

In all three cases, your email won’t be opened which contributes to lower open rates.

Thus, you need to keep three things in mind if you want high cold email open rates -

  1. being relevant to your prospect.
  2. stand out in their inbox and
  3. avoid spam traps set up by ESPs.

Here’s how to do that.

Keep your subject line relevant

Relevance trumps personalization, all the time. You can write the most engaging and most convincing email of all time but if someone doesn’t need your product or service they won’t buy from you. And in most likelihood, they won’t open your email in the first place.

Imagine you are walking through the aisles of a supermarket, how many times have you stopped in front of something that you don’t need? You stop only when you are either -

  1. planning to buy it right now
  2. planning to buy it soon or
  3. the product is so catchy that you want to check it out.

Similarly, for a cold email keep your subject lines relevant to their -

  1. current business circumstances
  2. their pain points or problems or
  3. their career/business goals.

Relevant subject lines will boost your email opens even if someone is not ready to buy immediately.

Keep it short

Lengthy subject lines shout “SPAM!”

And they are also more likely to be ignored by your prospects because they might come across as “yet another sale.” Or people might confuse them to be promotional or marketing emails.

Lengthy emails also make prospects think that replying to the email probably needs some higher levels of commitment from them. The reason is that humans have been wired to reciprocate in their daily transactions.

So if you write an email subject line that is verbose, your prospect’s brain indicates that this is either “spam” or a “high-commitment task” and decides to ignore it.

I don’t mean to say that long subject lines don’t work but then it has to be personalized and very relevant to them.

Pro-tip: Keep your subject lines less than 4 words, and ideally one or two words.

Pique their curiosity

Do you remember how some of the best products have excellent packaging? You need something similar for your subject lines. You have to get to a point where your subject lines are enticing enough to pique someone’s interest.

Since you are already relevant and are keeping your subject short, the next level is to use a word that arouses your prospect’s curiosity.

For example, you sent an email to the founder of a Series A company that has been rapidly hiring engineers. Your email subject line can be -

  1. relevant - by talking about their “engineering team” or “series A round”
  2. short - by limiting the subject to two to three words.
  3. arousing - by connecting relevance to a problem they might be facing like “engineering hiring support” or “dev collaboration” if you sell services for hiring support or a developer collaboration software correspondingly.

Connect it to your email preview

The email preview text is often ignored by anyone who writes a cold email. If you have come up with the perfect subject line you need to ensure that it is connected with the first line of your email.

This first line is often previewed in inboxes and will give your prospect an indication of what the email is all about or why have you reached out to them.

Tying up your email preview and subject line also reassures your prospect that you aren’t going to waste their time. In our above example, the subject could be “dev collaboration”, and the preview line could be -

Since you have been rapidly hiring developers post your Series A round, I reached out [first_name].

Avoiding the spam filters

Avoiding spam words in subject lines is quite a basic requirement if you want to land in the primary inbox. Yet with so much effort put into other areas of running a cold email campaign, people might end up missing this.

In short, all ESPs have spam filters in place and they use a sophisticated algorithm to qualify an email as spam or not. In that algorithm, one of the parameters is the use of spam words. Some words are more likely to be used in spam emails and ESPs understand that so they kind of downgrade your “spam or not” score when they see you have used such words in your subject.

Some of the words include but are not limited to - free, discount, sale, etc. For a complete list of spam words to avoid check here.

Examples of cold email subject lines

In this section, we discuss some high-level ideas to create subject lines that might get higher open rates.

Personalized subject lines for cold emails

Personalized subject lines are the best way to hit all the basics that we discussed above.

  1. They are relevant since they are personal
  2. You can keep them short
  3. They arouse the curiosity of your prospects
  4. Are easier to connect to the preview and
  5. Avoid spam filters since they are unique.

Some ways to personalize subject lines include -


People love their alma mater and if you can connect something from the university they attended to initiate a conversation it most certainly leads to a reply.

You can also use Clay or Open AI to create an intro line related to a news event that happened at the university. Here’s how Eric Nowoslawski leverages the university in his cold emails. Remember this is quite tough to do but if you can do it like Eric, you’ve got it.


If you are selling to marketers, sales folks, or founders talking about their target market often works wonders. Just type in a word or two about their target market and see your open rates boost.

You can figure out from their company descriptions what kind of companies they sell to. For example, someone might be selling to PE firms, just use “PE firms” in your subject line and see the magic unfold.

Pro-tip: Use Open AI APIs to figure out the ICPs of your prospects at scale.

[buyer persona]

Including job titles of a prospect’s buyer persona can also be useful for increasing the open rates of a cold email. Job titles indicate that you have researched the prospect and know who they target. This establishes trust and makes them open your email.


If you have prospects in niche industries, you can also mention their industry or the latest developments in their industry in the subject line. Niche prospects are less likely to receive emails with subject lines that talk about their industry. In that case, if you mention a recent big event or a new way of doing things that will work.

For example, you might be selling to marketers in pharmaceuticals and ChatGPT is a big change that came across. Use a subject line saying “pharma and ChatGPT.”

[mentioned in news]

LinkedIn Sales Navigator has a feature where you can filter people based on whether they have been “mentioned in the news” or not. Use this feature to create a list of such people. Then you can use scrapers, Clay, or Open AI APIs to find out the news outlet, or the topic mentioned in the news.

Next, you can cite your research on the subject.

[blog post]

Referencing a high-value post that someone is proud of can be a great way of catching their attention. Since a blog needs effort and they have made significant investments in it people are more likely to open an email when you talk about their blog.

[content on social media or other platforms]

This is quite similar to the above idea on blog posts. If you see someone’s social media post or Youtube video has high levels of engagement it probably means that it was valuable and also something that the creator is proud of. You can mention such posts or content in the subject lines to gain the attention of your prospects.

For example, “your LinkedIn post on emails” or “your cold email Youtube video” could be great subject lines for sending to someone creating content about emails.

Boring subject lines for cold emails

A counterintuitive way of writing email subject lines is to become boring as hell. When everyone is being creative with their subject lines being boring means you are the one that stands. Here are a couple of ways you can do that.

[service area]

Mention in a word or two how you are going to help your prospect. This could be something as simple as just your service area or the problem your product solves for your prospect. For example, if you are a growth marketing agency, send an email with a subject as “growth” “marketing support or “growth experiments.” It is to the point and relevant at the same time.

[product name]

If you are sending a first email to someone you can also just mention your product’s name along with a problem you solve. For example at earlyGTM, I can send an email with the subject, “earlyGTM x growth” or “earlyGTM x cold emails.”

Spintax usage in subject lines for cold emails

Spintax has been widely used for email copywriting but its usage in cold email subject lines is still limited. Neil Abraham has a great way of spinning subject lines. This ensures that you get to test variations while maintaining email deliverability.

Here are some ways you can spin subject lines, (courtesy of Neil) -

  1. Come up with 10 subject lines.
  2. Use spintax in your subject line field on Smartlead to add variance. Examples -
  3. {service} chat
  4. [name}, question
  5. {service} question
  6. question for {name}
  7. Chat about {service}
  8. question about {company}
  9. {company} x {your company}
  10. {company} and {your company}
  11. Loved your {personal accomplishment}

Question-based subject lines for cold emails

Asking relevant questions is a great way to get your emails opened. Here are some ways you can do it without coming across as dumb.

quick question

The often cited best subject line by cold email experts “quick question” ensures you get to introduce your product or service in a short email. You just have to make sure that you have a really meaningful question about their business or the problem you are trying to solve.

Remember you just get to ask one question. So make it meaningful.

[service area question]

You can ask a question about the problem you solve or the service you provide. Like “question about engineers”, or “question - app infrastructure.”

[unique insight-based question]

You can also find out some unique insights about your prospect’s business and ask a question about that. For example, you can research that they are using a particular tech stack and ask a question about it. Like use the subject as “MongoDB question” and then tie it up with an introductory line that points out that you saw that they use MongoDB and so on.

Subject lines invoking mutual connections

People buy from people they like and we like people who are like us.

Mutual connections are a great way of establishing that the degree of separation between you and your prospects is low. Then they have a reason to trust you and listen to you.

[X sent me to you]

Do this when you have a referral from someone and when “X” has specifically asked you to connect with your prospect. Never use this subject if you don’t have explicit consent from “X.”

[X was a past colleague]

If you have a mutual connection who was a past colleague or a past customer you can use that in a subject line to establish trust and pitch your product or service.

[I helped X do Y at Z]

If you have worked with a mutual connection and helped them fulfill a business objective share how you helped them accomplish it. Curiosity will lead your prospects to open your emails.

Value-based subject lines for cold emails

If you are in B2B you know everyone just wants to get their job done. Thus pointing out a specific problem or how you solve that problem can be a great way to gain the trust of your prospects.

[pain point]

Mention the pain point you are trying to solve in your. For example, “card reconciliation” for expense management, “valid leads” for sales intelligence, “ or “DevOps testing” for DevOps software.


You can also test your subjects by providing a word or two of your solution in the subject. From the example above, it can be - “automated reconciliation” for expense management, “ready to buy leads” for sales intelligence, “ or “AI-based testing” for DevOps software.

[solution implementation benefits]

Many prospects also jump to action if you lead with the benefits of your solution. From the example above, it can be - “hassle-free reconciliation” for expense management, “faster prospecting” for sales intelligence, “ or “all test cases covered” for DevOps software.

Testing cold email subject lines for best results - why should you test them?

Now that you have some ideas you need to understand that you won’t hit upon the best cold email subject line accidentally or in the first go. You might get lucky but sooner or later it will stop working.

That is why you need to develop a mindset of continuously testing subjects to find the best one that is working for a specific market & persona at a time.

A/B testing email subject lines

For A/B testing subject lines, you need to allocate some of your prospecting cadence to a base sequence and an experimental sequence. Say you learned of a new idea or learned something from last week’s campaign, this week you should try to allocate maybe 30% of your capacity to a new email variation with a new subject line.

By continuously testing subjects you will have a clear picture of what resonates with your prospects and then you can finally figure out the best cold email subject line for your campaigns.

But if you are someone who understands all this but doesn’t have the time to test through different variations. Or if you have tested with little to no success, I can help. Reach out to me at and I can point you in the right direction.

Till then, happy emailing!