Email Subject Lines: Characteristics, Types and Best Practices

Aqsa Mughees
Aqsa Mughees

Last updated on

March 17, 2023

Whether or not you believe it, you do get judged by the subject lines of your emails. So if you want your email content to be read and clicked, make sure your email subject lines are jazzed up, because as previously thought, subject lines are not just afterthoughts - but more important than the email body since they are said to be a marketer’s ticket for standing out in an overcrowded inbox.

Planning an email campaign? Mailmunch has everything you need under one roof. From interactive and fully optimized email templates to segmentation options and campaign analytics to track the performance of your campaign, you can design, send and analyze your email marketing campaigns with just a few clicks.

47% of marketers test their email subject lines for performance optimization because after all, even the best email is useless if it does not get opened. The best email subject lines are usually short and descriptive enough to trigger curiosity among the readers.

Why is an email subject line important?

The email subject line is like a book cover or an article headline. You need to compel the reader to click and read what’s in it otherwise, we all know, your offer, coupons, links all end up in the trash. 

So, for your emails to have a high open-rate, your subject line should strike a balance between being enlightening and entertaining. Just like with other digital content, in the process of inducing people to click, the subject line should never under-promise or over-promise what’s inside. Those that do not accurately represent what’s inside are assessed accordingly: 69% of recipients report emails as spam just based on their subject lines. 

So, especially if you are a new business, starting fresh, a powerful, punny, or funny subject line can make your brand establish an identity quicker because eventually, it is the strength of the brand that motivates people to click on your email. 

Characteristics of a good email subject line - The C.U.R.V.E approach

The Creative Director & Digital Strategy Director at Trendline Interactive, Alex Williams spent years writing and testing e-mail subject lines for business clients.

Based on experience, he created the C.U.R.V.E. formula, allowing him to create catchy e-mail subject lines that get opened almost every single time.

the curve approach - email subject lines

C.U.R.V.E. stands for Curiosity, Urgency, Relevancy, Value, and Emotion. A good subject line should at least have two of the C.U.R.V.E elements to get a high open-rate. 

So, without further delay, let’s dive in. 


A lot of times a subject line that sends out a clear message tends to have a high open rate, however, sometimes it is good to maintain a little secrecy to create curiosity for the recipient. 

The “mystery” tactic is known for its ability to pique the natural curiosity and interest of the recipient. It makes sense as well because such subject lines require opening the email to find out what exactly it offers, automatically resulting in a higher open rate

However, be sure to align your subject line with the overall brand persona, tone of voice, and target audience. You would not want to mislead the recipients or trick them into opening the email just for a high open-rate because let’s face it, it can badly backfire since the reader can mark you “spam” forever. Just remember, trust always comes first. 


Creating urgency is a great way for people to take an action. You can use this strategically to craft your email subject lines for a better response. 

For example, communicating the end of sale or promotion with phrases such as “Only 2 hours left” improves the chances for a user to at least go through the email once. 

This is also a good approach when planning a series of emails such as a countdown. However, make sure you do not continuously flood the inbox, coming off spammy. 

Urgency can be created for anything. Following are some relevant subject line examples:

  • A discount or special offer
  • A free live event like a webinar
  • Training program or product for a limited time only
  • A limited number of spots or items available for sale
  • News/tips related to a current event/situation

Keep in mind that urgency is only powerful when it’s associated with relevancy and/or value. Besides, your window of opportunity to get the attention of the reader is quite small, so a cleverly crafted email subject line that conveys urgency with powerful language or fast-approaching deadlines can do wonders. 


Whenever we subscribe to an email list, the purpose is to keep ourselves informed of the latest happenings or learn more about a particular topic. So, a subject line that is based on a trending topic of interest or an ongoing event can help you establish your brand identity and authority within the industry. 

You will not just get a competitive edge by offering information about something that is otherwise trending but will also pique the reader’s attention, intriguing him/her to click and know more. 

As easy as it sounds to create a subject line relevant to the interests of your subscribers, it takes quite an effort to do so, keeping in mind that with time people’s wants and needs change. 

What’s relevant today might not be relevant tomorrow. So, keeping up with your target audience through social media interactions, gathering, and updating customer data and information can serve useful here. 


Subscribers always look for the value your email offers them. Whenever you are thinking about writing an email subject line just ask yourself this question, “If I were the recipient of this email, would I find this valuable among so many other emails in my inbox?”

At the end of the day, it is the new things, experiences, cool offers, discounts, and relatable content that people dig for, especially when little or nothing is asked for in return. 

Terms like “free stuff” “coupon code” and “50% off” in the subject line tell the recipient that you have something exciting to offer them. However, terms such as “your favorite” or “for you” also intrigue the recipient as it shows that something valuable is inside.  


It’s nothing new to say that we as humans respond to and make decisions based on emotions, mostly. That is why it is important to trigger the right emotions in people, encouraging them to take action and open your e-mail.

One of the best ways to do that is to use sensory language. To do that, you must use words that connect with the five human senses (sight, sound, touch, taste, and smell). 

For example:

  • You haven’t seen anything like this before.
  • How many times have you heard these three words?
  • Why do we feel so bad after a breakup?
  • Nothing tastes better than a fresh macaroni pizza.
  • Does your bathroom smell bad? Here’s what to do.

Such power words have 10 times or even 100 times more emotional value than average words.

Even words that have the same meaning can have a different emotional value. For example, the word “cheat” is considered to have more impact than “unfaithful”. 

Types of Email Subject Lines 

The type of email subject line usually depends on the kind of business you have, the target audience, and the content inside the email. However, here is a list of main types of subject lines that you can incorporate to increase your open rates. 

1. Informational

Such email subject lines are usually to the point, concise, and give the main information so that the user opens the email for further details. 

informational email subject lines


Email subject lines that threaten scarcity tend to perform well because humans tend to have a fear of missing out on things. 

3. Personal

We all love personal touches in emails, right? These email subject lines usually include the recipient’s name, a small detail of a recent visit/purchase, or a recommendation.

personal email subject lines

4. How-to

How-to usually offer specific benefit to the reader. As long as the how-to email subject line is valuable and relevant to the audience, it can result in better open rates. 

5. Urgent

As mentioned earlier, these subject lines are action-oriented. They either create a sense of fear among the users or the anticipation of gaining something quickly. 

urgent email subject line

6. Local

Location-specific email subject lines tend to intrigue users to know what is happening around them even if they are not interested initially. It shows the user that you have done your homework and you know them well enough.  

7. Clever and interesting

If you know your audience well, a joke or relatable pun can be useful in making your email stand out. Make sure to not alienate your users by using a phrase that they cannot resonate with.

clever and catchy subject lines

8. Trendy

Everyone nowadays is on the lookout for trendy stuff, whether it’s fashion, lifestyle, tech, or sports. The latest fascinations are exciting for the readers to open your emails.

9. Short and sweet

Since 42% of emails are opened on mobile devices, a short and sweet email subject line should be the key. So, craft it in a way that your subject line gets the message across in 25 to 30 characters. 

A major part of writing a short email subject line is good editing by figuring out the words you don’t need and omitting them.

short and sweet email subject lines

10. Controversial

A controversy is quite attention-grabbing, right? However, it should be pulled off carefully, knowing your audience well enough to create a balance. Otherwise, it can backfire. 

11. Lists

Our brains are naturally drawn to numbers. That is why lists have become common as subject lines. Also, lists provide a snappy way of building interest. 

listicle email subject lines

12. Statistic

Considering how we are living in the age of digital media and the internet, everything is about numbers. Using statistics in your email subject lines is a great way to provide a proven, objective piece of information, naturally piquing curiosity.

13. Questions

Questions as a subject line can immediately engage users and create an instant dialogue. Keep them open-ended so that the reader cannot just simply answer with a “no” and move on. 

question subject line

14. Offer

Adding an offer in the subject line is one of the most effective and common ways to increase open rates, as the majority of subscribers are looking to get something valuable, whether it’s a discount or free things. 

15. Command

Using a command in your email subject line gives the reader clarity on what you expect them to do. Therefore, to encourage responses, command is an effective email subject line strategy. 

16. Keyword

This is more of a conventional and SEO-friendly way to soar open rates. Thinking and looking for words or phrases that people might type on google to search for something can prove to be fruitful and give you better searchability for your messages. 

Email subject lines - best practices

Since we have agreed on email subject lines being crucial in increasing the open rate, let’s consider the following best practices.  

email subject lines best practices

1. Keep it short and sweet

46% of the emails are opened on mobile devices. If they are too long, they automatically get cut off. Therefore, the email subject lines should consist of 50 characters or less for them to show completely. So try to avoid long words and unnecessary information.

2. Avoid “no-reply” email

People do not add no-reply or unfamiliar emails to their address book, considering how they get hundreds of spammy emails every day. Always use a familiar sender name for a more personal effect, since it gives the reader a feeling that they are talking to an actual person.  

3. Add personalization token

Everyone loves to see their name in the email subject lines. Not only does it give the reader a feeling of connection and importance, but also makes them believe that the email is specifically tailored for them. 

Besides, you can personalize using location as well, such as “Top bars in New York City you should go to.” Just see that you do not over-personalize because that can be creepy and backfire. 

Want to create a personalized email campaign? Mailmunch gives you complete control over your email marketing with the option to customize your emails and personalize them according to the preferences and choices of your target audience.

4. Avoid false promises

Building and maintaining customer trust is crucial to envision a long-term relationship. Therefore, you cannot promise something in the subject line which you are not offering in the email, since it is likely to decrease the open rate and increase the bounce rate and unsubscribe rate. 

5. Keep it action-oriented

Email subject lines are kind of a call-to-action because you want people to click on the email. Therefore, subject lines that begin with action verbs are more clickable and enticing. They encourage people to see what’s inside. 

6. Be funny and punny

Humor is a fun way to engage the user. People like to read light-hearted, funny content that they can relate to. Email subject lines that include puns are more likely to attract the user and make the brand likable. Make sure to not go overboard. In fact, here’s a rule: whenever you are confused, ask a coworker.

7. Practice A/B testing

A/B testing is one of the best ways to see which email subject lines perform better. Therefore, it is always a good idea to A/B test your email subject lines, and tweak the words according to your results. This way you can easily note if statements work better or if your audience finds questions more intriguing. 

8. Avoid overusing exclamation marks and caps

Overusing caps and exclamation marks can overwhelm the user as no one wants to get yelled at. Using question marks and exclamation marks together (i.e. Got a minute? Try this workout!) in one email subject line can also send your email to the spam folder. 

9. Use emojis

use emojis

Emojis add life to your email subject lines. They make your emails more relatable and appealing. Also, they make the audience understand your tone of voice in a better way and help you connect with them. 

Smart formulae for killer subject lines 

Although there isn’t any right or wrong approach to sending emails, since it is usually audience-dependent, however, these three formulas can help you create subject lines to increase click through rate. 

email subject lines smart formulae

1. What they want + what you have = mutual benefit

Whenever anyone opens their inbox, they are looking more for reasons to delete their email than keep them. So, you need to tell them why they should open the email with the appropriate email subject line. 

2. Personalized + the right tone = subscribers that feel valued

As mentioned above, using the user name, location, or any other thing that is personal in the email subject line is a great way to increase the open rate.

You can always use the additional information from the subscription form or pop-up to personalize emails. It implies that you actually recognize the recipient as a person to connect with and hence, builds trust. 

3. Timing + knowing your audience = higher open rates

Whenever you send an email, make sure to optimize your send times for the time zone that most of your readers are in. Prime sitting-on-the-couch time in the Eastern time zone is at the exact same time as rush hour on the west coast, so the timing does matter!

AI Copy Assist: Your friendly email subject line generator!

Still, we have you covered if you don’t know how to craft a subject line! Mailmunch introduces AI Copy Assist, an email subject line generator that allows marketers to craft trendy and creative subject lines. 

Just give AI Copy Assist a subject, a 200 character prompt, and generate multiple email subject lines. Also, you can add a bit of flair to your subject lines and get trendy, witty, and humurous subject lines.

Author Bio

Aqsa Mughees

Aqsa Mughees works as a Content Lead at Mailmunch with 5+ years of experience in creative content strategy. With a grip in digital content creation for the tech industry and an undying love for writing, she is crazy about helping businesses grow through content marketing.


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