How to write subject lines that will improve your open rate


Let’s say you’ve just written the body of a prospecting email, and it’s your best yet. Time to pop the cork and celebrate? Well not quite yet… you still have the subject line to go. 

The dreaded subject line, left until last, in the hopes that you’d have an email-subject-line-ephiany. 

There’s pressure to write an amazing subject line – it’s the make or break of your open rate. But unfortunately, we don’t have a ‘one size fits all’ formula, though we do have a few tips on how to write the best prospecting email subject lines.

What are you actually offering? 

Many companies use a sense of urgency or a promise of discounts to entice the recipient to open an email.  

For example:

However many businesses feel this tactic has run its course. Instead of encouraging a customer or client, the only thing they encourage is an eye roll. Not only that, but they risk your email coming up as “spam”. Financial terms like this can put your emails at risk of not even reaching your prospects main inbox. See Hubspot’s ultimate list of spam trigger words to avoid.

Rather than using this outdated spammy technique, write down what you are offering and base your subject line off that. 

Pro tip:

  1. Words like ‘partnership’ or ‘collaboration’ are more likely to lead to the email being opened, as they offer something for the recipient (that isn’t a discount!). 

Similarly, being genuine and authentic from the subject line will result in a higher number of opened emails. Contrary to popular belief, many (if not most) people can tell if the writer of an email is being genuine. One of the main things when writing the body of the email is to sound authentic and, well, human – carry this tone into the subject line for continuity and success. 

Word count

There is no hard and fast rule for how many words should be in your subject line.

It can be hard to know whether to stick to short subject lines, or add a few more words; both can be used effectively to add intrigue. It entirely depends on the email and prospect you’re trying to engage, but it’s generally a good idea to steer away from subject lines longer than 10 words. 

A short subject line for a short email may be a good rule of thumb, and you can always extend the subject line for the second email, particularly if they opened the first. 

Character count

Word count’s sneaky friend, character count, is more important than most people realise. Where the subject line gets cut off on the screen is almost always based on characters, rather than words; usually, the cut-off point is around 30 characters. 

It is for this reason that synonyms are important. Obviously, don’t get thesaurus-happy, but replacing the odd word could result in an increased number of emails opened. It’s also worth noting that words with more characters than their synonyms often have subtle differences in meanings, particularly with colloquialisms. 

For example, ‘quick chat’ and ‘brief discussion’ both imply the same thing, but the former seems much more informal than the latter, and the word ‘discussion’ implies that both parties talk to each other, rather than a one sided conversation. Perhaps for this reason, ‘discussion’ results in a higher open rate than ‘chat’. 


One of the biggest tips we can give is to personalise the body of the email as much as possible, so it seems less like a ‘send-to-all’ spam. However, this may not be the case for the subject line. 

Mentioning the company name of the recipient is no longer impressive. 

Research is a given nowadays, and it can easily be automated, leading the recipient to think that it is spam. Surprisingly, mentioning your company name, as the prospecting company, will have better results. 

There is, of course, a time and place for this, as it won’t fit with every email subject, however if you find yourself typing the prospect’s company name, stop and see if you can flip the subject line round to include your own name instead. As well as seeming less spam-like, it also shows transparency. The recipient immediately knows who the email is from, and this honesty is likely to improve open rates. 

One way in which personalisation can be useful is using the word ‘you’ or ‘your’. Using these words makes the recipient feel like you are talking directly to them, as a human rather than as a company or prospect. 

A way to do this is to ask a question, and is especially effective if you know the question is related to their company in some way. To avoid seeming like spam, this will require more research into your target audience, but could have brilliant results. 

Want to know more about personalisation? Check out our blog: Personalised B2B email templates tailored to your audience

Be vague

We know, we know: this is literally the opposite of our previous point, but that’s what we mean when we say there are no rules with subject lines. If personalising the subject with your company name or ‘you’ doesn’t work, perhaps vagueness will. 

Instead of directly referencing your product or service, mention something related to it but still general. ‘Quick chat’ is an example of this, as it is direct enough that you know the subject of the email, but vague enough to intrigue the recipient to open it. 

Use subject line tester tools

It’s true when they say there’s a tool for everything! Subject line testers can help give you an idea of how effective your subject line is, and can also show you how the email will look on various devices. 

Subject line testers:

TestSubject is the tool for you if you want to see how your email will look on different devices.

Email subject lines can be a real balancing act – it’s got to be ambiguous enough to evoke curiosity and a click, but not so obscure that the recipient just ignores it. A good exercise is to step into their shoes: imagine how you would react if you received the email, and use it as a case study. 

Obviously this isn’t the most accurate method, but it can give you a good starting point. Subject lines can be tricky, but with experimentation and analysis, you’ll certainly start to see results. Once you’ve created the perfect subject line, the next phase is sending it. 

Skip to the end…

Overall, it can be said that writing an effective subject line comes down to trial and error, as well as looking at what works for your specific industry. What works for Marketing and Advertising, might not work for Information Technology services so it’s always worth researching your target audience thoroughly! 

Here’s our top tips for writing the perfect email subject line to improve your email open rate:

  • 10 words or less
  • 30 characters or less
  • Use pronouns like ‘you’ and ‘your’
  • Try different methods if the previous one didn’t work well
  • Use a subject line tester tool

Outbase offers an automated solution for sending personalised emails on a large scale, meaning you don’t have to sacrifice quality for quantity. Outbase leaves you with the time to write high quality email subject lines that will guarantee a higher open rate.

Find out what we’re all about and sky rocket your sales. Start your free trial.

Written by:
Lily Ruaah Content Writer