Agency tips

The science of subject lines

• By acaboom-admin on January 6th, 2023 •

Want to learn how to attract attention to your emails? After all, 47% of people say they open emails based on the subject line alone. Whether you are sending a proposal to a client or a pre-appointment presentation – how do you get their attention? We asked our marketing lead Elaine Keep to tell us everything about subject lines. 

“The advice for many years for great copy has been to look at tabloids. When Celtic was defeated by Inverness Caledonian Thistle, the sharp-as-a-tack Paul Hickson wrote the famous headline – Super Caley Go Ballistic, Celtic Are Atrocious.

It explains the whole matter at hand in 7 words. It delivers it in such a funny and quirky way – it’s a winner. Every marketer, business owner and copywriter would love to have a Paul Hickson moment and pull something like that out of the bag. Still, for most of us, when it’s time to create the perfect opening line, it’s essential to focus on being not too clever but customer-centric. Accolades aren’t what you should strive for; opens and clicks are.

That said, without the perfect subject line or opener, you’re leaving custom on the table.

Let’s look at the top ways to maximize your chances of being seen in a crowded inbox.

Tap into emotion with your subject line

A good headline or subject line has to tap into human emotion – fear, excitement, curiosity – and use that to draw people in.

This is relatively easy, and you can start to spot them everywhere after a while!

  • Don’t open this email – curiosity
  • You might be missing out on this one – fear
  • James, your boss will think this took hours – sloth
  • We think you deserve more  – greed
  • This is what they do in London – excitement
  • James, your custom proposal is ready – excitement/ personalisation

Then try these formulas…

How to: 

  • How to increase commission – a 12-step plan


  • The six ways your property can stand out


  • Is your home better than these 5?

A guide to

  • A guide to better-looking doorsteps

Avoid mistakes

  • Avoid this mistake when selling


  • Everything you need to know about doorsteps

Here’s why 

  • Here’s why you should change your door colour

Increase your X with Y

  • Increase your chances of a sale with a new door colour

Stop doing this 

  • Stop using fake plants! Here’s why buyers hate them

This vs This 

  • Red doors vs. yellow doors

The Simple and Easy 

  • The easy guide to door colours

But keep an eye on the length 

Subject lines with 21-40 characters tend to see higher open rates, and you need to look at about six words.

Make it about them

When it comes to any content or copy you see, from toilet cleaner to the latest iPhone- the secret behind anything you read being successful is that you should feel it answers the question – what’s in it for me?

Personalization can be effective at doing this in such a small space and personalized subject lines (e.g., “Hey [Name], here’s the info you requested”) tend to have higher open rates than non-personalized ones.

Use power words

Power words sound great when you hear them and feel punchy. The more evocative and powerful descriptors you can use – the better. Here are some examples:

  • Instead of ‘new’, you can say ‘revolutionary’
  • Instead of  ‘different’, you can say ‘unbelievable’
  • Instead of ‘trusted’, you can say ‘proven’

Here are some more:

  • Guaranteed
  • Explosive growth
  • Limitless possibilities
  • Unlock
  • Ambitious
  • Explode
  • Breakthrough
  • Explosive
  • Genius

As you can see – they score highly!

Words that help open rates

  • Available
  • Better
  • Brand new
  • Breaking
  • Can
  • Celebrate
  • Easiest
  • Expiring
  • Fastest
  • Find
  • Important
  • Information
  • Introducing
  • Limited time
  • Really
  • Today only
  • Try
  • Won’t
  • You /Your

Avoid some words in case of spam filters

Spam filters always look for words and phrases that could indicate spam, so it’s important to avoid using them in your subject line. Commonly blacklisted words include:

  • Free
  • Guarantee
  • Deal
  • Cheap
  • Discount
  • Cash
  • Product
  • Sale
  • While you sleep

So, when crafting the perfect opening line or subject line, ensure you don’t include these – you can read this very large list here and see what to avoid.

Some great subject lines for your presentation and proposal sent through Acaboom

When you send a customer something they are expecting, that’s very similar to an ‘order confirmation’ email – the kind of thing you have probably got when you have ordered anything online. Luckily for you, this is one of the top-performing emails you can send, which is why Acaboom’s open rates are so high.

You still need to pick the right line for it, though. So, with the learnings from above to be personal and appeal to emotion, as well as using analysis from 7000+ campaigns sent to databases of more than 5,000 subscribers to find the top 5 subject lines for this kind of confirmation email, here are some ideas to accompany your presentation, appointment confirmation or proposal.

  • Thank you for booking your appraisal, James
  • James, ahead of your appraisal
  • Your appraisal confirmation + extra info
  • Appraisal confirmation – important info inside
  • Great news! We’re seeing you soon.
  • I’ve popped in something before we meet.
  • Wanted to make your market appraisal appt as easy as possible…
  • Your appraisal is booked. Here’s what’s next
  • Great to meet you, James- here’s what I learned about your property
  • Thanks for today, James
  • Your custom proposal – hot off the press
  • Attached, as discussed, is your proposal
  • Your proposal is now ready
  • James, please find your custom proposal

Want some great subject lines for property professionals based on data from other agents?

Many moons ago, I worked at an email provider who dealt with property clients sending thousands of emails daily to consumers. Take this with a pinch of salt, as this was a few years back, but my data at the time showed the following.

Emails with a 9% click-through rates and above went to themes around subject lines that said: 

  • Regional
  • Your Invitation
  • Sharing
  • Join Us
  • Get involved
  • Your local news for (town name)
  • Take Advantage

(All very inclusive words.)

80%+  of these emails that were un-opened were associated with these words:

  • Our award-winning
  • *Last minute*
  • Let us
  • We are
  • Our latest news

(All about the company, not the reader)

The largest volume of unsubscribes

  • “(Brands) (Month) Newsletter”
  • “A unique opportunity”

How to check your subject line before you commit to the send

There are many free online checkers that can analyse a subject line for you. Here are our top 2 freebies.

Refine by moosend is a free and helpful way to ‘guestimate’ what your best email subject line will be. 

You can also use Omnisend which gives various scores and even suggests different subject lines, again, this is free! 

When is the best time to send an email? 

To demonstrate that this question will never be answered correctly – let’s share some of the common advice.

  • “According to the data, 11 AM Monday is the peak time when people open their emails” – MailerLite
  • “The best days to send emails are Tuesday, Wednesday, and Thursday. Data analysed from 10 different studies indicated that Tuesday reigns supreme for shooting out marketing emails. ” – Engine Mailer
  • Friday is the best day to send emails, with the highest open (18.9%) and click-through rates (2.7%) (MooSend)

So – Monday, Tuesday, Wednesday, Thurdsay and Friday then.

What about the weekend?

  • “It turns out that the best time to send B2B emails is actually during the weekend; specifically on Saturday at 10 AM.” – Tidio

We jest – but as every platform uses its own data, it’s too hard to explore what works best with any real clarity. As with any marketing effort, it’s essential to test different subject lines to see which ones perform the best for YOU. What time is best for YOU?

Unfortunately, only doing the work will allow you to continually improve your email campaigns’ effectiveness.

The last bit of advice – don’t focus on the subject line!

MailChimp ran a 2022 analysis of click rates and found averages across all sectors of 2.62%. Focusing on the recipient experience when the email is opened has never been so important. Having a great subject line that makes 100% of people open is alright, but if what is inside is rubbish, you lose their trust, waste your shot and make it far harder for yourself next time.”

About Elaine Keep

Elaine Keep handles marketing at Acaboom and has worked with leading businesses and PLCs across Europe. She has over 14 years of marketing experience and has been head of marketing for brands such as Tuffnells and SVM Global; and is also content editor for the Incentive Marketing Association EU.