A scientific approach to outbound sales.

We believe that customer acquisition is an art, and we approach it with a lot of passion and creativity. However, we also believe that in order to do it well, we have to take it very seriously. And this means questioning and evaluating everything we do.

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Report 02

Crafting the perfect email subject line


There are a lot of steps you need to take to create an effective outbound sales campaign. However, it all starts with a subject line. And believe it or not, it might actually be the very first bottleneck of your outbound campaign.
How so? Even if you find prospects that are a perfect fit and bang out a top-notch, personalized email — if your subject line is weak, no one will open it which means, no one will read that great email that you wrote.
Just to put it in perspective. A weak subject line can result in a 20% open rate (OR), while a strong subject line can give you an OR as good as 60%, or better. As we’ll review below, our data scientists have found that a strong subject line can potentially give you 3 times more replies/leads/meetings from the same amount of emails sent.
The purpose of this report is to analyze what makes a great subject line. It will help you improve your open rates, and as a result, it will have a positive impact on the overall performance of your outbound campaigns.

What data did we consider?

For the purpose of this report, we analyzed over 4,498,185 emails along with their subject lines. Emails were sent by 443 organizations using Growbots between January 1, 2018, and September 1, 2018. The average open rate of analyzed emails was 48%.


The length of a subject line


The length of a subject line impacts the open rate. The longer the subject line the lower the open rate. Our findings show that the ideal subject line is only 4 words long – this length subject line performed best, with open rates as high as 60.17%.


According to our research, subject lines which exceed 15 words perform significantly worse than the ones below 15 words – their open rate drops to 31.56%.


4 words are enough to make the subject line appealing but short enough to fully display in your prospect’s mailbox. No wonder that longer subject lines perform worse, as 40% of emails are read on mobile devices.


For more details, have a look at the graph below.



“Quick question” subject line – does it actually work?


Many influential (and less influential) sources often recommend using the “quick question” subject line. It might have worked in, like, 2006, but is it still effective today?
Turns out, no.
Emails sent utilizing the quick question subject line had an open rate of 38%. Which is 20.83% below average. It is absolutely time to archive “quick question” to the Great Junk Folder in the Sky.


The power of personalization


All outbound sales experts claim that personalized subject lines work better. We decided to evaluate this claim using hard data, and here is what we found.


Subject lines with any kind of personalization tend to perform better than non-personalized ones. They get a 50% open rate which represents a 4.17% improvement over average.


How can you make the most of personalization, i.e. which custom fields are the most effective?


Subject lines which include a company name perform best – at 56% which represents a 16.67% improvement over average.


Additionally, if we combine this lesson with the previous finding about subject length, we are starting to see a major lift in performance. For example, a less than 5-words subject line, incorporating a company name custom field, will generate a 60% open rate – 25% improvement over the average.



Subject lines indicating that “you would like some of their time”


Subject lines which include a keyword indicating you would like some of your prospect’s time like mins/minutes, time, meeting etc. tend to perform worse than those without. For example, emails which included “time” in the subject line had an open rate of 30% while those without had an open rate of 48%, which is 47.92% below average.


There is an exception to the rule, however. Subject lines which contain the word “demo” or “call” work better than those which do not include any of the two. “Call” subject lines perform significantly better than the remaining subject lines, with an OR of 63%. This represents a 31.25% improvement over average.


Check out the graph below for more details.



Using deceptive subject lines


How about tricking your prospect into opening your email, will this work? Even if it did… do you really want to be THAT person? Good news, you do not have to lose sleep at night because the answer is NO. No it does not.


Using deceptive subject lines like adding “re:” or “fwd:” to your initial message, or “urgent”, “action required” will not only have a negative impact on your OR but it will also seriously annoy your prospects.


They have been tricked many times before, and they have definitely learned their lesson, so just quit it.


Subject lines which included “attention”, “urgent”, “action required” had an OR of 23% and performed 52% below average. While subject lines which included “Re/fwd/fw” had an open rate of 44% which is 8.33% lower than average.


The graph below includes more details on this subject.



Using marketing practices in your outbound campaigns


Sometimes marketers forget that sales emails are very different from marketing emails, meaning their outbound emails look too much like newsletters — which hurt their OR’s.


Including words such as “free”, “help”, “quick”, or numbers (e.g. “Want to boost your sales by 30%?”) have a detrimental effect on ORs.


Asking a question in a subject line has an OR of 36% and performs 25% below average.


The table below clearly demonstrates that subject lines which do not include any “marketing related” keywords perform significantly better than those which do.



Message preview matters


Your message preview (i.e. the part of the email your prospect views before opening it) impacts your open rate. Are you surprised? Well, do not be. We all get hundreds of emails a day and are actively looking to suss out irrelevant emails quickly, without missing relevant ones. Your prospects are adept at quickly scanning a preview line and deciding if it is worth their time.



We have decided to analyze the first 70 characters displayed in the email’s body, and here is what we found.


Starting your email with generic statements usually has a negative impact on your open rate. These statements include:

  • Being apologetic (“sorry/apologies/pardon/excuse”) – which has an open rate of 34% which is 29.17% below average.
  • Being polite (“hope you’re well/everything is well”)- which has an open rate of 38% which is 20.83% below average.
  • Introducing yourself (“My name is/I am/I’m”)- has no positive or negative impact on your open rate which stands at 49%, but represents a wasted opportunity as it does not add any value to your prospect
  • A pleasure to meet you – this is an interesting one, as it has got a whopping open rate of 87% which is 81.25% above average. It is a risky approach, however, as you are indicating to your prospect that you got introduced to them. Being deceptive will have a negative impact on your campaign’s performance. Your prospect might open the email but will probably unsubscribe immediately.

At Growbots we believe that the most effective previews are personalized, catchy and interesting enough, to make your prospect want to find out more.


Key findings and recommendations

The length of a subject line impacts your open rate, the shorter the better as 40% of emails are read on mobile devices. According to our research, subject lines which have 4 words perform best at 60.17% (OR) and represent 25.35% improvement over average. Subject lines which exceed 15 words perform the worst. Personalize your subject lines, try to make them short and catchy.
Using the “quick question” subject line might have worked in the past, but is no longer effective. It has an OR 20% lower than average.
Personalization has a positive impact on ORs. As a matter of fact, subject lines with any kind of personalization perform better than subject lines without personalization. They have an OR of 50% which is 4.17% better than average. Subject lines which include a company name have proven the most successful and represent a 16.67% improvement over average.
Asking for a bit of your prospect’s time will usually hurt your open rates unless you include the words “demo” or “call” as both of them tend to perform at 16.67% and 31.25% above average, respectively.
Do not use deceptive subject lines, they will not only hurt your ORs (performing at 52.08% below average) but they will definitely make your prospects unsubscribe from your future emails. It is just not worth it.
Sales emails are not like marketing emails, you should avoid using words like quick, free, and using numbers as on average they perform worse than emails which do not include these words.
Do not forget about the email previews. They actually impact your ORs. Avoid generic opening lines as they can hurt your OR (or at the very least will not improve it). Use opening lines which provide value to your prospects; make them personal and catchy.

A special bonus

Since sharing is caring, we have got a little bonus for you. Here are 10 subject lines that have very satisfactory (to say the least) open rates. All of them were created by our customers and sent via Growbots. Feel free to steal them if they suit your needs, you have got our permission!


Behind the scenes

This report was delivered to you by Growbots. We are the team behind the first platform that streamlines the entire process of getting meetings with new potential customers. We bring together sales prospecting and outreach into one tool, providing our customers with results like:

When you’re starting from scratch:

87 meetings with Fortune 500 brands and $1M deal closed in 1,5 month

case study
When you want to improve your existing process:

10x reduced time spent on prospecting and customer acquisition cost

case study

Want to learn more about our solution?
Request a demo below!


Kasia Kowalska

Content Marketing Manager @ Growbots

Mac Wiatrak

Data Scientist @ Growbots

Chris Zawisza

Head of Demand Generation @ Growbots

All data summary

Here you can find a summary of all test we've run in order to write this report. Feel free to share it with your friends and colleagues!

deceptive keywords like "attention", "urgent" or "action required"23%-52.08%
keyword "mins" or "minutes"25%-47.92%
keyword "free"26%-45.83%
including percentage value27%-43.75%
keyword "time"30%-37.50%
preview - "sorry/apologies/pardon/excuse"34%-29.17%
including any number36%-25.00%
including questionmark36%-25.00%
preview - "hope you’re well/everything is well"38%-20.83%
"quick question"38%-20.83%
keyword "help"41%-14.58%
keyword "quick"42%-12.50%
keyword "meeting"42%-10.42%
"Re:", "Fwd:", "FW:" prefix44%-8.33%
day of week or "tomorrow"47%-2.08%
preview - "my name is/I am"49%+2.08%
any custom field50%+4.17%
{{company_name}} custom field56%+16.67%
keyword "demo"56%+16.67%
{{company_name}} custom field and fewer than 5 words60%+25.00%
keyword "call"63%+31.25%
prieview - "pleasure to meet, nice to meet"87%+81.25%