A Comprehensive Guide to Creating Captivating Cold Email Subject Lines

Created On
August 29, 2023
cold email subject lines guide

A total of 347.3 billion emails are sent and received every day. This statistics is a stark reminder of how crowded the email recipient's inbox is.  

How to stand out? 

The answer is the subject line. If you want to see good results on the analytics dashboard of your cold email tool, learn how to craft catchy subject sentences. 

Read this cold email subject line guide till the end to find A to Z about subject lines for cold email campaigns. 

In this blog post, I have discussed about 

  • The importance of subject lines  
  • The secret to creating a killer subject sentence
  • The key elements of a good subject sentence
  • Different approaches of creating subject lines for cold emails
  • Test subject sentence with A/B testing
  • Common mistakes 
  • Compliance and legal consideration


Let's jump right in! 

Why are Subject Lines Important in Cold Emails?

The email marketing industry is one of the most competitive spaces in recent times. With a total of 347.3 billion emails sent and received every day, it is challenging to catch the recipient’s eye. This is where subject sentences come in. 

When the inboxes are overflowing with messages, the humble cold email subject line plays a pivotal role in determining whether your carefully crafted email gets the attention it deserves. 

Looking for ready-made subject lines?
Check out “80 Cold Email Subject Lines to Increase Your Response Rate”.

Think of it as the virtual equivalent of a firm handshake and an engaging smile – it’s the first impression that can make or break your chances of initiating a meaningful conversation.

So, here are the few points that make subject sentences so important in cold email marketing:

  • Increase open rates
  • Create the best first impression
  • Stand out in a crowded inbox

Increase open rates

The primary purpose of a cold email subject line is to entice potential customers to take that crucial step and open your email. Consider it the gateway that stands between your email and the hellish fate of spam triggers. 

A well-crafted subject line can ignite curiosity, evoke interest, and even trigger emotions that prompt recipients to click and explore further.

For example:

Ryan, how about a 5x ROI boost?

If somebody is struggling with ROI, the above subject sentence will catch their attention instantly. They might or might not take the desired action, but they will definitely want to look at the email body. 

Create the Best First Impression

Think about it—when you open your inbox, what catches your eye first? 

It's not the sender's name, not the email's content, but that little nugget of text right at the top—the subject line. 

In a matter of seconds, your recipients will make a snap judgment based on that subject sentence alone. It's like meeting someone for the first time; the initial impression lingers and can influence the course of your relationship.

Here’s an example of how you can do it. 

{Competitor} gained {result} using {tool name}

This type of subject lines create the best first impressions. This tells your recipients

  • Shows the result
  • Reveals competitor’s secret behind their success
  • Gives assurance 

Stand Out in a Crowded Inbox

In today's digital age, standing out is not just a challenge, it’s a necessity. With inboxes flooded with emails ranging from work updates to discount offers, your cold email must do more than just appear in the recipient's list.

It needs to command attention. That's where creativity comes into play. Crafting a subject line that stands out amidst the sea of mundane subject sentences requires a unique blend of creativity, strategy, and understanding of your audience.

You can do that with catchy email subject lines. Sometimes, referring to popular culture in your subject sentences can also do wonders. Here are some subject line examples.

  • Be the Dwight of your sales team
  • That’s what the client said

Your subject line sets expectations for the content inside; it's a promise you must fulfill with valuable content and a genuine intent to establish a personal connection.

So, next time you find yourself struggling to write those perfect subject sentences, remember its significance. It's not just a few words—it's your foot in the door, your introduction, and your opportunity to make a lasting impression. 

Take the time to craft subject lines that resonate with your recipients, and you'll find the doors of engagement swinging wide open.

Secret to Crafting Killer Subject Lines—Research

When it comes to creating subject lines that stop recipients from scrolling past your email, research is the only weapon you have. It's the key to unlocking the door to your audience's minds, and crafting subject sentences that resonate on a personal level.

Read this section to learn how to do it. 

Understand Your Audience Inside Out

Imagine walking into a conversation without knowing anything about the person you're speaking to. That's exactly how sending an email without audience research feels. 

Delving into your target audience's pain points, interests, and preferences is like donning a detective's hat before crafting your subject lines. It’s about becoming intimately familiar with what makes your audience tick. 

The bottom line is—know your audience inside out. You can do this by checking your customers’ conversations with the customer support team. 


Think about it—would you be more likely to open an email that speaks directly to your needs and interests, or one that seems generic and vague? 

Audience research allows you to fine-tune your subject sentences so they resonate with your recipients. It's the art of showing that you understand them, their challenges, and what they're seeking.

Focus on ICP, Buyer Personas & Customer Surveys 

Ideal Customer Profile and buyer personas are the big guns when it comes to audience research. 

Buyer personas and ICPs are like blueprints of your ideal customers, offering insights into their demographics, behaviors, and preferences. They're the foundation upon which you can build laser-focused subject lines. 

And then there are surveys, the direct line to your audience's thoughts. These gems of feedback can provide insights into pain points, desires, and even the words and phrases your audience uses. Armed with the right wordings, you can create subject sentences that feel like they're coming from a friend, not a faceless corporation.

Key Elements of an Effective Subject Line for Cold Email Outreach

Crafting an attention-grabbing subject line for cold emails is an art that involves combining several key elements. Think of these elements as building blocks that come together to create a subject line that not only intrigues but also compels recipients to click the "open" button.


Imagine walking into a store with a confusing sign—you'd likely walk right back out. The same goes for your subject line. 

Clarity is the foundation upon which engaging subject lines are crafted. It's about letting recipients know what's in it for them right from the get-go. Nobody likes guesswork, so make sure your subject line clearly states the purpose of your email. For example:

This tool will help with the expansion


Humans are naturally curious creatures. Tap into that curiosity by crafting subject lines that evoke questions, tease ideas, or hint at valuable information. Think of it as leaving a trail of breadcrumbs that leads recipients straight to your email CTA. 

By sparking curiosity, you're encouraging recipients to take that extra step and take the desired action.

{Competitor company} uses {tool/service}

The secret to 5x boost in ROI


A subject line that resonates is one that addresses the recipient's needs. Your audience is looking for solutions to their problems, so your subject line should clearly show how your email offers value. 

Make it clear that you understand their pain points and are offering a solution or insight that's tailored to them.

High spam rates? Smartlead can help


There's something inherently attention-grabbing about seeing your own name. Incorporating the recipient's name in the subject line adds a personal touch that sets your email apart from the generic crowd. It's like addressing someone directly in a crowded room – it captures their attention and makes them feel valued.

Mark, is there too much on your plate? Try automation


FOMO (Fear of Missing Out) is a real psychological trigger. Creating a sense of urgency in your subject line can be incredibly effective. 

Whether it's a limited-time offer, a webinar registration closing soon, or an upcoming event, the idea that time is running out can nudge recipients to open the email before it's too late.

You need to check this out before the spring sale

Last chance to win 10% off in yearly plans

Different Approaches for Crafting Subject Lines

Crafting subject lines that entice recipients to open your cold emails requires a bit of artistry and a dash of psychology. Let's explore four different approaches that can make your subject lines stand out in the sea of emails.

Curiosity-Driven Subject Lines

Curiosity may have killed the cat, but it's a marketer's best friend. Using curiosity in subject lines is like leaving a trail of breadcrumbs that leads recipients into your email. 

Pose a question, hint at something intriguing, or tease an unexpected twist. The goal is to create an itch they can't help but scratch. For instance:

Guess what we discovered about your industry?

This one secret can transform your productivity

Showcasing Value

Recipients open emails when they know they'll gain something valuable. Benefit-oriented subject lines for emails focus on what's in it for them. 

Highlight the outcomes, solutions, or knowledge they'll gain by opening the email. It's like holding a shiny reward in front of them. For example:

Double your website traffic with these strategies

Unlock insider tips to boost your sales

Trying to write the perfect email copy?
Steal one from 101 Cold Email Templates to save your time. 

Making it Personal

There's magic in a name. Personalized subject lines go beyond the generic and address recipients by their name. It's a signal that the email was crafted just for them. 

Think of it as striking up a conversation at a party—it's more engaging when someone addresses you directly. Examples include:

Ryan, here's a special offer just for you

Samantha, your opinion matters to us

Triggering Action

Urgency and scarcity are powerful motivators deeply embedded in human psychology. These subject lines convey that time is running out or a valuable opportunity is limited. 

It's like signaling, "Act now, or you might miss out!" Such subject lines include:

Last chance to secure your spot in our webinar

Only 24 hours left for this exclusive discount

Remember, these approaches aren't mutually exclusive; you can often combine elements to create even more compelling subject lines. The key is to align your approach with your audience and the message you're conveying. 

Experimentation is your best friend. Test different approaches, gauge responses, and fine-tune your strategy based on what resonates best with your recipients.

Test Subject Lines with A/B Testing

A/B testing isn't just a fancy term; it's the secret sauce that can take your cold email subject lines from good to extraordinary. This is the perfect method to test two different subject lines and see which gets better metrics and engagement.

Setting Up A/B Tests: Simple Steps

  • Segment Your List: Divide your email list into smaller segments. This ensures that your test is conducted on a representative sample.
  • Create Variations: Craft two subject lines: the control (A) and the challenger (B). These can be different approaches or variations of the same idea.
  • Random Allocation: Assign each subject line to a segment randomly to ensure a fair test.
  • Track and Measure: Send out your emails and monitor open rates for each subject line.

Curious to learn more about A/B testing?
Read The Ultimate Guide to Cold Email A/B Testing to learn more. 

Interpreting the Results

Don’t judge a subject based on open rates. Focus on click-through rates, response rates, especially positive response rates. 


Email marketing is continuously evolving, which means what works today might not work tomorrow. That's where continuous optimization comes in. 

Analyze your A/B test results and apply the insights to future subject lines. Adapt, refine, and evolve based on data.

A/B Testing Tips

  • One Variable at a Time: Test only one element at a time, like the wording or length of the subject line, to accurately attribute results.
  • Sample Size Matters: Ensure your sample size is large enough for meaningful insights. Too small, and the results might not be reliable.
  • Regular Testing: Make A/B testing a regular practice. Trends change, and so should your subject line strategy.

A/B testing subject lines is like peeling back layers to uncover the essence of what resonates with your audience. It's about replacing assumptions with evidence and making decisions based on data.

Common Mistakes in Cold Email Subject Line Copies

Crafting effective subject sentences for cold email campaigns is an art, but it's also about avoiding the pitfalls that can affect your efforts. 

Let's dive into some common mistakes that can derail your subject line game and how to steer clear of them.

Clickbait Conundrum: Promising More Than You Deliver

Using misleading language that promises more than your email can deliver is a classic clickbait mistake. While it might tempt recipients to open initially, it can lead to disappointment and erode trust when they realize the content doesn't match the hype.

This mistake has a higher chance of emails landing in spam, leading to higher bounce rates and spam rates. 

Lengthy Lament: Overloading with Words

Subject lines that resemble a mini-novel are a surefire way to get ignored. Lengthy subject lines not only get cut off in email previews but also overwhelm recipients. Keep it concise and to the point – a teaser, not a thesis.

The ideal subject line shouldn’t be more than 21 characters or five to six words. 

Spammy Language: The Red Flags

Subject lines packed with spam-triggering words like "urgent," "exclusive offer," and excessive exclamation marks can land your cold emails straight into the spam folder. Using such language can damage your credibility and render your efforts futile.

Lack of Relevance

Subject lines that feel disconnected from the recipient's needs or interests are destined to fail. Your subject line should be a bridge that connects their pain points to your solution. Irrelevant subject lines will lead your email messages directly to the junk folder. 

Generic Greetings: The One-Size-Fits-None Approach

Subject lines that lack personalization come across as mass-produced and impersonal. 

Avoid using generic greetings like "Dear Sir/Madam" or "To Whom It May Concern." Instead, address recipients by their name or other personalized details.

Use “Ryan, you need to see this” kind of greetings to create personalized emails. 

Overusing Capitalization and Punctuation: A Loud Shout

Subject lines written entirely in capital letters or with excessive punctuation (!!!) can be off-putting. They come across as shouting rather than engaging, and recipients might perceive them as aggressive or unprofessional.

Inadequate Testing: Skipping the Proofreading

A minor typo or a grammatical error can dent your credibility. Skipping proofreading and testing can result in subject lines that not only look unprofessional but might also fail to convey your intended message.

Compliance and Legal Considerations

When crafting compelling cold email subject lines, it's not just about grabbing attention—it's also about keeping it legal. Understanding the legal norms is crucial to ensure your emails don't get caught in the spam filters or worse.

Keep the following points in mind to avoid any legal issues. 

Comply with CAN-SPAM Act 

In email marketing, the CAN-SPAM Act (Controlling the Assault of Non-Solicited Pornography And Marketing) stands as a guidepost. It applies to commercial emails and mandates certain practices to protect recipients from deceptive or unsolicited messages. 

While the Can-Spam Act is specific to the United States, adhering to its guidelines will prevent you from violating similar legislations like GDPR, the Australian Spam Act, Canada's Anti-Spam Legislation, and others.

Use Accurate Sender Information

One of the hallmarks of compliant email marketing is transparency. Your subject line might entice recipients to open your email, but the sender information reassures them about its legitimacy. 

Always use a recognizable and accurate sender name and email address. Misleading recipients about who you are can lead to mistrust and can even lead to legal consequences.

Provide Opt-Out Mechanism in Emails

Including an opt-out mechanism is not just a legal obligation; it's a sign of respect for your recipients' preferences. Every email you send should include a clear and simple way for recipients to unsubscribe from future emails. 

Ignoring unsubscribe requests or making it difficult for recipients to opt-out not only violates regulations but also damages your reputation.

Final Thoughts

And there you have it, the ultimate guide to crafting captivating cold email subject lines that'll make your cold emailing shine in the sea of cluttered inboxes. Remember, your subject lines are the gateway to engagement and success.

Whether you're weaving curiosity, showcasing value, or adding a personalized touch, the key is to be creative, strategic, and relevant. And don't forget the legal compass – following the CAN-SPAM Act and prioritizing transparency is a must. 

So go ahead, experiment, learn, and watch your email outreach reach new heights. Don’t forget to create sequences for follow-up emails. 

Happy subject line crafting!

What’s a Rich Text element?

The rich text element allows you to create and format headings, paragraphs, blockquotes, images, and video all in one place instead of having to add and format them individually. Just double-click and easily create content.

  • dfbvrsg
  • svsv

Static and dynamic content editing

A rich text element can be used with static or dynamic content. For static content, just drop it into any page and begin editing. For dynamic content, add a rich text field to any collection and then connect a rich text element to that field in the settings panel. Voila!

How to customize formatting for each rich text

Headings, paragraphs, blockquotes, figures, images, and figure captions can all be styled after a class is added to the rich text element using the "When inside of" nested selector system.

Author’s Details

Rajnish Das

Rajnish Das is an in-house writer at SmartWriter and SmartLead. She writes product-oriented, data-driven content for B2B SaaS audiences and educates them on marketing and sales topics. Her expertise includes outbound marketing techniques like cold emailing and LinkedIn outreach.


Edited by:

Charu Mitra Dubey


Frequently asked questions

General Questions

What are active leads?

Active leads are the contacts you upload in Smartlead, similar to contacts in HubSpot; if you upload 1000 leads to a campaign, they are considered 1000 active leads. If you upload similar leads to a new campaign, they are not considered a “new active lead” as they already exist in our system.

Do you provide mailboxes, or do I need to connect my own?

We don’t offer mailboxes yet. You need to get your own dedicated list of mailboxes using popular providers like Gmail, Outlook, Zoho, and others that exist in the market. Once you get them, follow our detailed guides to connect them quickly.

Do you offer guides and articles on succeeding with cold emails?

Absolutely, one of our most popular guides can be found right here. It's been used by a large percentage of users to go from zero to cold emailing experts. Covering all topics from email infrastructure to copywriting and lead sourcing.

Is another tool needed for warmups?

No, Smartlead has over 200,000 highly reputed mailboxes connected. The advantage you get along with naturalized AI conversations is access to aged domains you will never find in any warmup tool.

What is the API commonly used for?

It is used popularly by agencies to automate their entire lead generation process as well as to connect Smartlead to external tools to push and pull data from. You can also connect to 1000s of apps using Zapier.

What type of businesses sees the most success with Smartlead?

Anyone that can close deals from demos will succeed with Smartlead. It works for Sales companies, Marketing agencies, SaaS businesses, Recruitment, and offline companies (like construction).

Do you provide me with lead sources?

We do not provide you with leads. You will need to use other data providers. These leads can be automatically added to Smartlead using our API or bulk uploaded via our CSV upload system.

Do you integrate with any CRMs?

We're building native integrations with Hubspot, Salesforce, Close, Pipedrive, and many more. The best part, due to our open API and Webhook infrastructure, you can connect to any CRM in the world without an issue.

How many team members can I add?

You can add an unlimited number of team members, as well as assign them roles and authority access.

Do you have custom plans beyond the Pro plan?

Yes, it's common for many people to move to Custom plans after a few weeks. You can view all the options for up to 10M leads on the subscription page once you sign up for free.

Powerful Automated Email Marketing that Drives Sales.

  • All Features Included
  • No Credit Card Required
  • Free Warmup Included