15 Cold Email Subject Line Do's and Don'ts

Created On:
January 29, 2024
Updated On:
March 13, 2024
dos and don'ts of cold email subject lines

People may or may not judge a book by its cover, but they do judge an email by its subject line. A subject line for cold emails is the first impression of you as a marketer/seller.  

According to statistics, 33% of email recipients open emails depending on the subject line, and adding personalized information is likely to increase open rates by 50%. 

Bottomline—subject lines are crucial for cold emailing, and crafting one can be trickier than you think. 

This article contains 15 cold email subject lines DOs and DON’Ts. 

Let’s dive in. 

15 Cold Email Subject Line Do's and Don'ts

If you’re wondering how to write better subject lines, here are 15 dos and don'ts of cold email subject lines to consider. 

Things you need to DO to craft the best subject line for cold email campaigns:

  1. Keep subject lines text-based
  2. Keep it within 30 to 45 characters (4 to 6 words)
  3. Personalize
  4. Always conduct A/B testing
  5. Refer to pain point
  6. Provide a hint about the email body
  7. Add a sense of urgency
  8. Use power words

Things you should NOT do while crafting a subject line for cold email campaigns:

  1. Don’t use sales-y language
  2. Don’t use all CAPS
  3. Don’t ask for a favor
  4. Don’t use emojis
  5. Don’t use special characters and too many numbers 
  6. Don’t mislead recipients
  7. Don’t use spammy words

Read this article till the end to learn about the above points in detail. 

8 Do's of Cold Email Subject Line 

Consider the below points as email subject lines best practices. Also, note that experimenting is the way to ace outbound sales. So, always, always conduct A/B testing to find what works and what doesn’t for your target customers. 

Find a tool like Smartlead that comes with A/B testing features, and you’re good to go. 

Let’s dive into the subject line crafting best practices. 

#1 Keep subject lines text-based 

Using special characters or excessive numbers in cold email subject lines can trigger spam filters because they resemble common tactics used by spammers. Spam filters often interpret such elements as attempts to manipulate or deceive recipients. 

To maintain authenticity and improve deliverability, it's crucial to keep subject lines text-based, avoiding tactics that mimic spam patterns. This ensures that legitimate emails are more likely to reach recipients' inboxes and enhances the overall effectiveness of cold email campaigns.

#2 Keep it within 30 to 45 characters (4 to 6 words)

Keeping cold email subject lines within 30 to 45 characters (4 to 6 words) is beneficial as short lines grab attention quickly, increasing open rates. They're mobile-friendly, ensuring easy readability on small screens. Examples: 

Brandon, up for 30% reply rate?

Jon, check this out

Secret behind Peakora’s 40% reply rate

According to stats, xy% of users open emails through mobile phones. Using short subject lines makes your email mobile-friendly, increasing your chances of a higher open rate.

These concise lines avoid beating around the bush and express the intention behind the email directly, enticing recipients to open emails promptly. 

#3 Personalize

Personalizing email subject lines is vital as it increases engagement by making the subject line relevant to the recipients. Customization can involve using the

➡️ recipient's name

➡️ referencing specific details about their company

➡️ tailoring the message to their interests. 

Including relevant information in the subject line establishes a connection, increasing the likelihood of the recipient opening the email. This personal touch creates a more meaningful and compelling first impression, ultimately leading to higher open rates and a better chance of achieving the desired response in cold email outreach.

#4 Always A/B Test 

A/B testing involves comparing two versions (A and B) of a variable of an email, like a subject line or opening line, to determine which performs better. 

In cold email campaigns, A/B testing is crucial to optimize subject lines for maximum engagement. It helps identify the most effective language, length, or personalization, refining strategies based on real-time data. 

Go for cold email tools like SmartLead that come with A/B testing features. Along with A/B testing, Smartlead also offers unlimited warm-ups, mailboxes, and a master inbox. This comprehensive solution enhances efficiency, ensuring your cold email campaigns are not only personalized but also backed by data-driven insights for continual improvement.

#5 Refer to the pain point

Referring to recipients' pain points in cold email subject lines is one of the most important dos of cold email subject lines, as it immediately captures their attention and relevance. Examples:

  • "Solve Workflow Woes with {Your Solution}"
  • "Boost Efficiency: Conquer Data Overload"

By addressing challenges or concerns specific to them, you demonstrate an understanding of their needs, establishing a connection. This empathetic approach makes your email more compelling and increases the likelihood of the recipient engaging with the content. 

Focusing on pain points establishes a common ground, showcasing your solution as a valuable resource tailored to address their specific issues, ultimately improving the effectiveness of your cold email outreach.

#6 Provide hint about the email content

The best email subject lines provide a hint of the email's content to set clear expectations and entice recipients to open the message. Recipients are more likely to perceive it as relevant and worth their time when the subject line offers a glimpse into the email's purpose or value proposition. 

This transparency establishes trust and encourages engagement, as recipients appreciate knowing what to expect. Crafting subject lines that align with the email's content improves open rates and contributes to a positive recipient experience in cold email campaigns.

#7 Add a sense of urgency

Adding a sense of urgency in subject lines is crucial because it prompts immediate attention and action. Time-sensitive language compels recipients to open the email promptly, fearing they might miss out on a valuable opportunity or limited-time offer. Examples:

  • "Limited-Time: Unleash Productivity Power Now"
  • "Act Fast: Exclusive Software Upgrade Available"

This psychological trigger creates a heightened interest, increasing the likelihood of engagement. By emphasizing urgency, you create a compelling reason for recipients to act swiftly, driving the desired response and improving the overall effectiveness of your cold email campaigns.

#8 Use power words

Power words are persuasive and emotionally charged terms that evoke strong responses. Incorporating them into cold email subject lines is essential to capture attention, evoke curiosity, and drive action. 

Power words trigger emotions, making your message more compelling and memorable. 

Subject line examples with power words are:

  • Create lead lists in 3 clicks only
  • Revolunatize cold email game with master inbox

7 Don'ts of Cold Email Subject Line 

If there’s a list of cold email subject line best practices, it would be filled with DON’Ts. One can craft the perfect subject by only focusing on the below points. 

From warning against emojis to spammy words, the below listed DON’Ts of subject lines will help you ace the cold emailing game. 

#1 Don’t use sales-y language

Sales-y language in a cold email refers to pushy, overly promotional, or aggressive wording that focuses solely on selling a product or service. Using such language can lower open and reply rates because recipients may perceive it as insincere or spammy. 

Buy this {tool} to increase ROI by 40%

Don't Miss Out: Unbeatable Software Savings

Additionally, it can increase bounce and spam rates as spam filters often flag emails with overtly promotional content. To improve email deliverability and engagement, it's crucial to strike a balance, using language that is personalized, relevant, and focused on providing value to the recipient.

#2 Don’t use all CAPS

Using all caps in subject lines can harm engagement metrics. While it may initially grab attention, all caps can be perceived as aggressive or spammy, leading to lower open and reply rates. Recipients read subject lines in all caps in a “yelling” tone. 

Additionally, email providers may interpret it as spam, increasing bounce and spam rates. Modern email filters prioritize user experience, and excessive use of all caps is a common characteristic of spam, potentially causing your emails to be flagged or sent to spam folders, reducing overall deliverability.

#3 Don’t ask for a favor

Asking for a favor in a cold email subject line can be off-putting and may lead to lower open rates. Strangers are more receptive to initiating conversations or providing value rather than being immediately asked for assistance. 

Can you help me with a review?

 I need your help

Marketers should focus on building relationships by offering insights, solutions, or relevant content, creating a foundation for meaningful interactions. This approach fosters a positive impression and increases the likelihood of recipients engaging with the email, ultimately leading to more fruitful long-term connections.

#4 Don’t use emojis

Using emojis in B2B email subject lines may appear unprofessional and diminish the credibility of the message. Emojis are often associated with casual communication and might be perceived as gimmicky or unprofessional in a B2B context. 

In business communications, maintaining a balance between a formal and serious tone is crucial for establishing trust and professionalism. Emojis could potentially be misinterpreted or not align with the professional expectations of B2B recipients, making it advisable to avoid them in cold email subject lines targeting the B2B space.

#5 Don’t use special characters and too many numbers 

Avoiding special characters and excessive numbers in subject lines is crucial to prevent triggering spam filters. Many spam detection algorithms identify these elements as common tactics used by spammers to manipulate or deceive recipients. 

❌ Unlock Exclusive Discounts Now!!!

❌ Increase ROI by 50% - Act Fast!!!

Using too many numbers or special characters can lead to your emails being marked as spam, reducing deliverability. Keeping subject lines clean and text-based ensures that your emails are more likely to reach recipients' inboxes, improving the chances of engagement and avoiding the negative impact of spam filtering.

#6 Don’t mislead recipients about the email content

Emailing recipients with clickbait subject lines can damage trust, credibility, and brand reputation. Clickbait is misleading and often leads to disappointment when the content doesn't fulfill the promised value. Over time, this erodes the trust of your audience, leading to disengagement or even unsubscribes. 

Building authentic relationships is crucial in cold email marketing, and using clickbait can undermine this trust, negatively impacting your long-term relationship with your audience. For sustainable engagement, it's essential to maintain transparency and deliver on the expectations set by your subject lines.

#7 Don’t use spammy words

Avoiding spammy words in subject lines is crucial to prevent emails from being flagged by spam filters and to maintain credibility with recipients. Spammy words trigger spam filters and may lead to lower deliverability rates. Some of the examples of spammy words are "guarantee," "free," "earn money fast," "limited time," and excessive use of exclamation marks. 

You can increase the chances of your emails reaching recipients' inboxes and foster trust with your audience by avoiding such spammy words. 

Final Thoughts

A short, personalized subject line that does not include spammy words but touches the recipient's pain point is ideal for cold email campaigns. It is tricky to get it perfect in one go. 

I recommend following the above DOs and DON’Ts of cold email subject lines. To find the perfect subject line, I suggest doing A/B tests.

A/B testing various subject lines or different versions of the same sentence will help you understand what works and what doesn’t with your target audience. Check out Smartlead for an easy A/B testing feature. 

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:


Frequently asked questions

General Questions

What is Smartlead's cold email outreach software?

Email automation FAQs- Smartlead

Smartlead's cold email outreach tool helps businesses scale their outreach efforts seamlessly. With unlimited mailboxes, fully automated email warmup functionality, a multi-channel infrastructure, and a user-friendly unibox, it empowers users to manage their entire revenue cycle in one place. Whether you're looking to streamline cold email campaigns with automated email warmups, personalization fields, automated mailbox rotation, easy integrations, and spintax, improve productivity, or enhance scalability with subsequences based on lead’s intentions, automated replies, and full white-label experience, our cold email tool implifies it in a single solution.

What is Smartlead, and how can it enhance my cold email campaigns?

Email automation FAQs- Smartlead

Smartlead is a robust cold emailing software designed to transform cold emails into reliable revenue streams. Trusted by over 31,000 businesses, Smartlead excels in email deliverability, lead generation, cold email automation, and sales outreach. A unified master inbox streamlines communication management, while built-in email verification reduces bounce rates.
Additionally, Smartlead offers essential tools such as CNAME, SPF Checker, DMARC Checker, Email Verifier, Blacklist Check Tool, and Email Bounce Rate Calculator for optimizing email performance. 

How does the "unlimited mailboxes" feature benefit me?

Email automation FAQs- Smartlead

Our "unlimited mailboxes" feature allows you to expand your email communications without restrictions imposed by a mailbox limit. This means you won't be constrained by artificial caps on the number of mailboxes you can connect and use. This feature makes Smartlead the best cold email software and empowers you to reach a wider audience, engage with more potential customers, and manage diverse email campaigns effectively.

How does Smartlead as a cold emailing tool can automate the cold email process?

Email automation FAQs- Smartlead

Smartlead’s robust cold email API and automation infrastructure streamline outbound communication by transforming the campaign creation and management processes. It seamlessly integrates data across software systems using APIs and webhooks, adjusts settings, and leverages AI for personalised content.

The cold emailing tool categorises lead intent, offers comprehensive email management with automated notifications, and integrates smoothly with CRMs like Zapier, Make, N8N, HubSpot, Salesforce, and Pipedrive. Smartlead supports scalable outreach by rapidly adding mailboxes and drip-feeding leads into active campaigns Sign Up Now!

What do you mean by "unibox to handle your entire revenue cycle"?

Email automation FAQs- Smartlead

The "unibox" is one of the unique features of Smartlead cold email outreach tool, and it's a game-changer when it comes to managing your revenue cycle. The master inbox or the unibox consolidates all your outreach channels, responses, sales follow-ups, and conversions into one centralized, user-friendly mailbox.

With the "unibox," you gain the ability to:
1. Focus on closing deals: You can now say goodbye to the hassle of logging into multiple mailboxes to search for replies. The "unibox" streamlines your sales communication, allowing you to focus on what matters most—closing deals.

2. Centralized lead management: All your leads are managed from one central location, simplifying lead tracking and response management. This ensures you take advantage of every opportunity and efficiently engage with your prospects.

3. Maintain context: The "unibox" provides a 360-degree view of all your customer messages, allowing you to maintain context and deliver more personalized and effective responses.

How does Smartlead ensure my emails don't land in the spam folder?

Email automation FAQs- Smartlead

Smartlead, the best cold email marketing tool, ensures your emails reach the intended recipients' primary inbox rather than the spam folder. 

Here's how it works:
1. Our "unlimited warmups" feature is designed to build and maintain a healthy sending reputation for your cold email outreach. Instead of sending a large volume of emails all at once, which can trigger spam filters, we gradually ramp up your sending volume. This gradual approach, combined with positive email interactions, helps boost your email deliverability rates.

2. We deploy high-deliverability IP servers specific to each campaign. 

3. The ‘Warmup’ feature replicates humanized email sending patterns, spintax, and smart replies.
4. By establishing a positive sender reputation and gradually increasing the number of sent emails, Smartlead minimizes the risk of your emails being flagged as spam. This way, you can be confident that your messages will consistently land in the primary inbox, increasing the likelihood of engagement and successful communication with your recipients.

Can Smartlead help improve my email deliverability rates?

Email automation FAQs- Smartlead

Yes, our cold emailing software is designed to significantly improve your email deliverability rates. It enhances email deliverability through AI-powered email warmups across providers, unique IP rotating for each campaign, and dynamic ESP matching.
Real-time AI learning refines strategies based on performance, optimizing deliverability without manual adjustments. Smartlead's advanced features and strategies are designed to improve email deliverability rates, making it a robust choice for enhancing cold email campaign success.

What features does Smartlead offer for cold email personalisation?

Email automation FAQs- Smartlead

Smartlead enhances cold email personalisation through advanced AI-driven capabilities and strategic integrations. Partnered with Clay, The cold remaining software facilitates efficient lead list building, enrichment from over 50 data providers, and real-time scraping for precise targeting. Hyper-personalised cold emails crafted in Clay seamlessly integrate with Smartlead campaigns.

Moreover, Smartlead employs humanised, natural email interactions and smart replies to boost engagement and response rates. Additionally, the SmartAI Bot creates persona-specific, high-converting sales copy. Also you can create persona-specific, high-converting sales copy using SmartAI Bot. You can train the AI bot to achieve 100% categorisation accuracy, optimising engagement and conversion rates.

Can I integrate Smartlead with other tools I'm using?

Email automation FAQs- Smartlead

Certainly, Smartlead cold email tool is designed for seamless integration with a wide range of tools and platforms. Smartlead offers integration with HubSpot, Salesforce, Pipedrive, Clay, Listkit, and more. You can leverage webhooks and APIs to integrate the tools you use. Try Now!

Email automation FAQs- Smartlead

Is Smartlead suitable for both small businesses and large enterprises?

Smartlead accommodates both small businesses and large enterprises with flexible pricing and comprehensive features. The Basic Plan at $39/month suits small businesses and solopreneurs, offering 2000 active leads and 6000 monthly emails, alongside essential tools like unlimited email warm-up and detailed analytics.

Marketers and growing businesses benefit from the Pro Plan ($94/month), with 30000 active leads and 150000 monthly emails, plus a custom CRM and active support. Lead generation agencies and large enterprises can opt for the Custom Plan ($174/month), providing up to 12 million active lead credits and 60 million emails, with advanced CRM integration and customisation options.

Email automation FAQs- Smartlead

What type of businesses sees the most success with Smartlead?

No, there are no limitations on the number of channels you can utilize with Smartlead. Our cold email tool offers a multi-channel infrastructure designed to be limitless, allowing you to reach potential customers through multiple avenues without constraints.

This flexibility empowers you to diversify your cold email outreach efforts, connect with your audience through various communication channels, and increase your chances of conversion. Whether email, social media, SMS, or other communication methods, Smartlead's multi-channel capabilities ensure you can choose the channels that best align with your outreach strategy and business goals. This way, you can engage with your prospects effectively and maximize the impact of your email outreach.

Email automation FAQs- Smartlead

How can Smartlead integrate with my existing CRM and other tools?

Smartlead is the cold emailing tool that facilitates seamless integration with existing CRM systems and other tools through robust webhook and API infrastructure. This setup ensures real-time data synchronisation and automated processes without manual intervention. Integration platforms like Zapier, Make, and N8N enable effortless data exchange between Smartlead and various applications, supporting tasks such as lead information syncing and campaign status updates. Additionally, it offers native integrations with major CRM platforms like HubSpot, Salesforce, and Pipedrive, enhancing overall lead management capabilities and workflow efficiency. Try Now!

Email automation FAQs- Smartlead

Do you provide me with lead sources?

No. Smartlead distinguishes itself from other cold email outreach software by focusing on limitless scalability and seamless integration. While many similar tools restrict your outreach capabilities, Smartlead offers a different approach.

Here's what makes us uniquely the best cold email software:

1. Unlimited Mailboxes: In contrast to platforms that limit mailbox usage, Smartlead provides unlimited mailboxes. This means you can expand your outreach without any arbitrary constraints.

2. Unique IP Servers: Smartlead offers unique IP servers for every campaign it sends out. 

3. Sender Reputation Protection: Smartlead protects your sender reputation by auto-moving emails from spam folders to the primary inbox. This tool uses unique identifiers to cloak all warmup emails from being recognized by automation parsers. 

4. Automated Warmup: Smartlead’s warmup functionality enhances your sender reputation and improves email deliverability by maintaining humanised email sending patterns and ramping up the sending volume. 

Email automation FAQs- Smartlead

How secure is my data with Smartlead?

Ensuring the security of your data is Smartlead's utmost priority. We implement robust encryption methods and stringent security measures to guarantee the continuous protection of your information. Your data's safety is paramount to us, and we are always dedicated to upholding the highest standards of security.

How can I get started with Smartlead?

Email automation FAQs- Smartlead

Getting started with Smartlead is straightforward! Just head over to our sign-up page and follow our easy step-by-step guide. If you ever have any questions or need assistance, our round-the-clock support team is ready to help, standing by to provide you with any assistance you may require. Sign Up Now!

How can I reach the Smartlead team?

Email automation FAQs- Smartlead

We're here to assist you! You can easily get in touch with our dedicated support team on chat. We strive to provide a response within 24 hours to address any inquiries or concerns you may have. You can also reach out to us at support@smartlead.ai

Powerful Automated Email Marketing that Drives Sales.

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