Myth-Busting Subject Line Best Practices

Katie Kalafus
March 14, 2022
 min read

Subject lines are critical to the success of your sales email strategy. Not only are they the most important factor driving your email open rates but they’re also your first impression with new customers. And with over 300 billion business and consumer emails sent per day; it’s critical to stand out from the crowd.


There are loads of studies out there on what makes a subject line “good”-  – however, their findings are often conflicting (or confusing). Just trying to figure out where to start can feel overwhelming.

In this article, we’ll dive into some of the data to give you our take on the advice that’s worth following, as well as the advice that’s better left ignored. 


While subject lines can appear similar to titles, is it best practice to capitalize each word, as you would typically do in the title of a blog or article?  

The data: Way back in 2016, Fast Company cited a study where they found that using the same subject line with all words capitalized had a higher open rate (54.3%) compared to the same subject line used with all lower-case (47.6%), concluding that perhaps there’s more authority conveyed when using capitalization.  

On the flip side, sales influencer Justin Michael more recently claimed his best performing subject line across millions of emails (used by 100+ startups) was a single, lower case word  – “growth”.  

Conclusion: Too close to call!

Depending on the type of persona you’re targeting, they may be more receptive to lower-case subject lines, as shown by the example above with startups. Personas that tend to be more formal (CFOs or cybersecurity experts, for example) might respond better to capitalization.


It’s worth A/B testing the Title Case, Sentence case and lowercase versions of your subject lines to discover which performs better with your particular sales strategy and buyer personas.  

Whatever style you decide to use, definitely DON’T USE all caps for email subject lines – as Hubspot notes, it feels like you’re being yelled at and looks more like a spam email when scanning an inbox.  

Using symbols & characters

When it comes to using characters outside of the standard alphabet, what’s best practice? Will the use of symbols or characters drive up open rates?

The data:  Constant Contact notes that excessive use of …, !!! and ??? or other symbols can get your emails flagged as spam, and Hubspot notes that you’re more likely to get flagged for spam when you use both a question mark and an exclamation mark in the same subject line.  

On the other hand, the use of a single question mark in your subject line may pique curiosity and have a powerful effect on your open rate. In 2021, Yesware found that subject lines that are questions generate on average a 10% higher open rate compared to other types of subject lines.

In the same Yesware study, the following 5 examples yielded open rates over 85%:

  • “What more could you want?”
  • “Why [Company]? And why now?”
  • “Are you ready?”
  • “[Name], is there too much on your plate?”
  • “What would you do with [Number] more hours per week?”

Sales influencer Josh Braun recommends using “{problem}?” or “{emotion} this?” as  subject lines, reasoning that people are “hard-wired to avoid problems” and pain.Braun’s examples include “failed payments?” or “annoyed by this?”

Conclusion: Use moderation.

While it’s pretty clear that you should stay away from weird symbols or overuse of characters in subject lines, we recommend using a single question mark with a short subject line. A single question mark in the right context can help drive interest in your email, so long as the words it follows are also relevant to your recipient.  

Emojis 😃😎✌️

The data: Although there isn’t extensive data available on emojis (yet),  there seems to be consensus around moderation. It’s also important to consider the formality of your target audience when deciding whether or not emojis should be used at all.  

HubSpot likes the use of a quirky emoji, as does MailChimp, but they recommend using only one emoji at time as a supplement (not replacement) to the words in your subject line. This helps  ensure that your message is clear.  

Conclusion: In moderation ⚖️

There aren’t a lot of examples of emojis making an impact on open rates, so at this time we don’t believe this is a best practice. However, if your buyer personas use them a lot in their own messaging and content (marketers, for example), it might be worth testing out using a single emoji as a way to stand out in a crowded inbox. Be sure to run a few tests because emojis can look different depending on how they’re viewed.🥳 

Using numbers

Okay, it’s pretty obvious that a weird symbol or emoji seems risky, but what about using numbers in a subject line?

The data: According to Yesware’s 2021 study, it’s a resounding yes. The study showed that including numbers in your subject lines generated a 45% higher open rate than the average. The psychology here might be that numbers are easier to understand and perhaps stand out in a crowded inbox.  

Outreach agrees, and notes that touching on data that isn’t about your product helps to build trust with your potential customer.  

Conclusion: 1,2,3, Go!  

If numbers are relevant to your target persona (perhaps tied to your value proposition or pain point), definitely try including them in your subject lines to see if it boosts open rates.  Yesware had a great idea for where to find some number inspiration: if you’re going to include a link to a case study in your email, pull an exciting metric from it, for example “175 hours /Month Back”.

First Name in subject line  

As Dale Carnegie famously said, “A person's name is to that person, the sweetest, most important sound in any language.” So, using a recipient’s first name in a subject line should be a no brainer, right?  

The data: Most research on this subject indicates that using someone’s first name in the subject line can drive higher open rates, plus it’s an easy way to add personalization at scale. For instance, Hubspot currently claims that emails that contained the first name of the prospective customer in their subject line had higher click-through rates than emails that did not.

However, this might be a trend that’s coming to an end. In 2021, SalesLoft released data that showed using a  recipient’s name in the subject line is causing a 12% reduction in the reply rate – just try looking through your spam email box and see how many have your first name in there.  

Conclusion: Avoid.

Delight your potential customers with something new and challenge yourself to think of other ways to make your email subject line feel relevant to your prospective customers. Instead of the subject line, start your email with a friendly “Hey {first name}.”

Tip: When it comes to using acronyms and abbreviations, we like this rule of thumb. If someone needs to look up what your subject line means, they are already an annoyed prospect. If your intention is to get your character count shorter, try using a thesaurus to find a shorter version of that word instead of shortening the word itself.  

Ideal Length  

Is short the sweet spot? What is the ideal word count or character count?

The data: With almost 50% of emails being viewed on mobile screens, keeping your subject lines concise is important to make sure the full message comes across; Yesware recommends limiting subject line length to 50 characters or less and under 7 words, noting that 1-5 words had the most success.  

Hubspot also recommends using fewer than 50 characters to optimize for mobile viewing. Salesforce advises the same 50-character length goal, noting that “Your goal should be to use as few characters as necessary in order to provide a message of value to your readers.”

Conclusion: Short is sweeter.

This is one best practice that is almost universally agreed on, but there can be some variation on exactly how short is best. At we see the best results with 2-word subject lines, but we coach our customers to experiment with using a variety of subject lines between 1-7 words in length.

Be ruthless and take out any erroneous words. For some extra motivation, here’s a fun stat: SalesLoft saw an 87% higher reply rate when using a single word in the subject line.  

CTA in subject line

While we know that every sales email should have a clear CTA, is it okay to put it in your subject line?

The data: Hubspot notes that “subject lines that begin with action verbs tend to be a lot more enticing”

Outreach claims a 75% open rate with “The Quick Call (Personalized)” subject line – so there could be something said for a CTA that’s to the point.  

Outreach also claims a 52% open rate with the simple request subject line “Connect?” but also noted its  decline from a 71% the year before, indicating its use might be oversaturated.  

“Any response would be appreciated” was a previous top subject line for Outreach, with a 65% response rate.  

Conclusion:  It depends.

If your CTA is short and relevant, it could be worth testing. But asking for something before someone gets to know you and your solutions could  seem a little pushy, so tread carefully and get feedback from your team before using a CTA in your subject line.  

Key Takeaways for Writing Effective Subject Lines:

Trends and best practices for email subject lines change all the time, but the best subject lines are going to be concise, relevant, and/or pique the curiosity of your prospective customer.  

To make sure your content is reaching customers you should be continually monitoring your open rate metrics and testing and iterating a few new subject lines every 3-6 months.  

Here at we see the best performing subject lines generating a 40-50% open rate. However, if in the first few weeks of a new campaign you are seeing less than a 20-30% open rate on your subject lines, scrap that subject line and start testing with a new one.  

At the end of the day, while subject lines might pique initial interest, to create a successful sales campaign you must ensure your email content is truly relevant to your recipient.  Before you begin a new email campaign, make sure you identify the persona, pain point, and value proposition you are targeting, and then see which subject lines would be the best opening to tell that story.  

When editing email content and subject lines in, be sure to use the First Line view (shown below) and Mobile View to see how your subject lines will look to prospective customers in an inbox or mobile phone.  

Lastly, if you're a customer needing help brainstorming new ideas for subject line, try out the subject line generator in our AI Assistant module or you can always reach out to your friendly Customer Success team to schedule a content strategy session.  

Extras resources:
HubSpot marketing: The Ultimate List of 394 Email Spam Trigger Words to Avoid in 2021
HubSpot report (free download): 100 Email Subject Lines We Actually Clicked
Salesforce: The Ultimate Guide to Using Emojis in Email Marketing

Share this post

Prospect with precision

Put your prospecting on Auto-Pilot, using