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The best email subject lines for prospecting (based on 4 million emails)

Posted on: April 14, 2020

Reading Time: 9 minutes

Category: Email content

The best email subject lines for prospecting (based on 4 million emails)

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Are subject lines your biggest hurdle to success? We’ve analysed four million email subject lines and can exclusively reveal what gets those emails opened, and what leaves them forever unread.

Note: for the very latest on subject line best practice, based on the analysis of 75.2 million emails, download The State of Prospecting 2024 whitepaper.

Let’s assume you’ve leapt over the initial deliverability hurdles and your brilliant message now sits in the inbox of your ideal prospect.

All they’ve got to do is open it.

Just one click and you’ve got another lead diving head first into your sales funnel, another success for your sales outreach strategy.

So how do you go about optimising open rates?

What informs the decision to open a prospecting mail?

Well, a glance at your inbox can only give you so much to go on.

You’ve got:

  • The Subject Line
    ‘[New Blog Posts] Google Ranking Factors +GA Tracking Mistakes’
  • The Sender’s Display Name
    ‘Joshua Hardwick [Ahrefs]’
  • And the Send Date/Time
    ‘05/03/2020, 22:30’

And that’s it.

Which is why the subject line can be a critical deciding factor in that open rate.

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What other factors can be in play?

Of course, even with a killer subject line, your targeting plays a massive role.

If you’re targeting the wrong audience there is no clever copy that will deliver the silver bullet.

But assuming your targeting is working, a great line plays a huge role in securing email opens.

Let’s look at how you can best hit home.

Our prospecting subject line and open rate study

To produce our study on the best email subject lines for prospecting, we’ve dusted down four million emails from the Sopro vaults.

From recent efforts to campaigns stretching back to 2017, we’ve crunched the data and chewed over the results.

And we found…

(Drum roll)

Subject lines make a difference. But they aren’t quite as critical as they are sometimes made out to be.

That’s not to say they doesn’t matter. But it’s just one of a huge number of factors that go into a successful email lead generation campaign.

Conquering deliverability challenges, identifying the perfect prospects and writing a message that connects are just as significant when it comes to the overall success of any prospecting campaign.

Here’s the thing.

The average open rate across 4,021,310 emails was:


Across the 50-odd variables that we applied to these emails, the range of open rates mainly fell between:

28.8% and 32.7%

That’s a difference of 11.9% between the lowest and highest open rate.

Percentage increments like this really matter when it comes to the end results. And if you add them up with all the other areas you can optimise, it can be the difference between a successful campaign and one that falls flat.

So let’s see where the gains are and the drop-offs can be found.

What characterises the best prospecting subject lines?

Word count

  • How many words make up the best subject lines?
  • When do you say too little and when have you said far too much?

With the yellow line representing the 31.2% average open rate, you can see that it’s best to either opt for super short (two-word) lines or aim for between five and 10 words. More then ten and the open rate rug is pulled from under your feet.

Across our four million prospecting emails the best results were registered by ten-word subjects, although nine-, eight-, five- and two-word subjects were not too far behind.

Character count

Not all two-word subject lines are equal.

For instance, there’s a world of difference between ‘Quick chat’ with its short, snappy informality and ‘Managing uncertainty’ with its cryptic message and more formal tone.

In opposition to word count, here we see a clear preference for fewer characters (or fewer and shorter words).

Certainly, anything over 61 characters is much more likely to be left languishing in the inbox. If you must use a few words, keeping them between 46 and 60 gives you a little lift (compared to sticking to between 31 and 45).

But fewer than 15 characters is where the real money is at.


This is where our results fly in the face of established marketing know-how.

How many times have you been told that all communication must be personalised and that doing so will bring you better results?

OK, you can stop counting – it was a rhetorical question, really.

With prospecting emails, we found that personalisation in subject lines consistently resulted in reduced open rates.

That’s across the board, whether the subject line was personalised by name, company name or by date (i.e. a mention of the day the mail is sent or a day to call).

It’s possible that the use of a company name or a prospect’s first name is increasingly perceived as a spam tactic.

Personalising the subject line may have run its course for prospecting. The results suggest that the average prospecting email will achieve a 31.2% open rate. Personalised subject lines drop this to 29.3%, and as low as 28.9% if the personalisation used is the person’s name.

Mentioning the prospecting company’s name

As we’ve seen mentioning the company’s name in a subject line results in a lower-than-average 29.3% open rate.

However, we also discovered that mails that use the prospecting company’s name are, somewhat counterintuitively, much more likely to get opened.

They return a 32% open rate.

That’s higher than the average and significantly higher than personalising by the potential prospect’s company name.

Why might this be?

We think this is related to the suggested perception of subject line personalisation as spam.  Mentioning who the mail is from gives transparency – there’s no trickery here. It is honest and frank – and as such it builds trust.

We all love mail that has ‘nothing to hide’.

You and yours

If personalisation by variables is largely ineffective, one classic marketing tactic still holds its own: the use of ‘you’ or ‘your’ in the subject line.

Prospecting mails with a personal address in the subject line yielded 35% open rates.

This is much higher than the 31.2% average – and suggests we should stop cramming data-driven personalisation into our subject lines and adopt a simpler approach to speaking directly.

Asking questions

Increasingly questions (or at least question marks) in subject lines are likely to spring spam traps.

But questions do work.

A subject line with a question in it charts a 32.5% open rate.

This is, as far as differentials in the subject line that is used go, a significantly higher rate than the average (31.2%).

Unlike with personalisation – and despite a similar association with spam – the use of questions in subject lines confirms established marketing wisdom.

Quick chats (and other brief conversational invitations)

We saw before that the two-word subject line carries some clout.

Typical of these is the formulation ‘Quick chat’. It’s informal, inviting, creates an air of mystery and it promises a low barrier (‘quick’) to engagement.

But does it work?

What’s shown here – from left to right – are the open rates for:

  • All variations that mention quick or brief chat – including those with text following the invitation (e.g. ‘re automation at |company|’)
  • All variations that mention brief chat – including those with text following
  • Only subject lines that contain just ‘Brief chat’ and nothing else
  • All variations that mention quick chat – including those with text following
  • Only subject lines that contain just ‘Quick chat’ and nothing else
  • Any subject line that mentions discussion
  • Any subject line that mentions meeting or meet

Compared to the average these invitations do not significantly differ – indeed, if anything, they are less effective.

The exceptions here are:

  • ‘Brief chat’ used on its own
  • And, interestingly, anything that asks for a discussion.

Subject lines that promise a discussion have an open rate of 36.8%. Such offers tower above the 31.2% average.

It may well be that chat – as invitingly informal as it is – lacks the dialogue and maturity promised by discussion.

Equally a discussion is a million miles away from the suggestion of selling – it may, as such, invite a warmer initial response to the mail.

Partners and partnerships

Another phrase that evokes a sense of dialogue and participation is ‘partnership’.

We looked at the open rate for prospecting mails that used either ‘partner’ or ‘partnership’ in their subject line and found another prospecting gem.

Such subject lines achieved an average open rate of 45.1%.

That is 45% higher than our average and definitely a candidate for further exploration.

Mystery prospecting subject lines

Is there any currency in an abstract subject line – does an air of mystery invite opens?

Before answering this question, let’s just give some examples of what we considered an abstract prospecting subject line to be.

  • Who’s in control the bank or the customer
  • Water cooler moment
  • VR/L&D
  • Time for coffee
  • This year’s content strategy…
  • Summer start – brief chat
  • Storytelling at *|COMPANY|*

All of these fail to explicitly nail their colours to the mast – preferring to sail close to the winds of mystery.

So, do they do the job?

Yes, they do. In terms of opening mails – prospects like to be enticed with subject lines that evoke rather than invoke.

The open rate for these hit 31.7% (against an average of 31.2%).

What are the best subject lines to use for prospecting emails?

There are a lot of factors that will influence prospecting campaign results more than subject lines alone.

But without an open there’s simply no chance of a prospect becoming a lead.

The best ways to secure those opens are:

  1. Keep subject lines super-short (two words) – or hit the middle ground of five to 10 words
  2. However many words you use, a character count of 0 to 30 is preferable
  3. Ditch personalisation in favour of announcing your own company – or opt to use ‘you’
  4. Use questions and mysterious subject lines – these can work just as well as transparency
  5. Mention partnerships and discussions – these get opened much more than inviting a quick chat

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