How to write email-opening subject lines

Still the best digital channel for return-on-investment, email can be a brilliantly effective and direct means of connecting with potential customers – especially in the era of mobile. Consequently, it's fiercely competitive.

Subject lines, as the first few words standing between a customer and your message, are the key to achieving cut-through in such a high-volume channel. Yet it's clear from many email campaigns doing the rounds that sufficient time isn't always invested in composing these priority pieces of microcopy.

There's no fixed formula for crafting a killer subject line. An email's success is influenced by multifarious and converging factors, some of which are changeable or outside of our control, making it difficult to glean a true measurement of its performance. Such as the time a recipient opens it, the device on which they're reading it, where they're reading it, and the mood they're in while doing so. If a customer has a bad experience with a brand's outlet, say, the last thing they want to see pop up soon after is a shouty sales message.

We also don’t know what else is happening in their inbox. According to Econsultancy’s 2015 email marketing census, the proportion of retail companies sending more than 1m emails a month is steadily rising, with a 7% increase in the last five years – so it’s safe to say that consumers are being inundated. There are, however, things within our control – including dispatch time, frequency, message strategy and not least the words themselves. Putting aside the technical innovations, tools and test-beds, there are some simple, tactical copy considerations that can have a significant effect on your open rates.

So, here are six things to consider before penning a subject line. . .

1. Persuasiveness

Some of the most persuasive language is also very basic. As we've found in many of our email campaigns, powerful verbs can prompt action. Take this example:

Get your voucher for 20% off food

Here ‘get' is tied up with the benefit, presenting the promise of an immediate reward with a decisive call-to-action – and so a compelling reason to open – to motivate the reader. Typically, we find that subject lines featuring ‘get' elicit a higher open rate.

The use of a pronoun (‘your') adds to the line's effectiveness by directly attributing the offer to the recipient. It conveys a more personal message and makes them feel involved in the communication from the start.

Verbs and pronouns combined can evoke immediacy, but there are more obvious ways to create a sense of urgency. If there's a time limit on an offer, say, being overt about this can help compel recipients to open on the spot, rather than leaving it until later (to be buried under newer email).

Also, in multiple-email campaigns or re-sends where the message offers a continued reward, such as a sale or special event, a tiered approach can refresh a subject line's appeal and provide the recipient with renewed impetus to open:

Get 20% off your next Harvester meal
Get 20% off your bill – just four weeks left
Don't miss out on 20% off
Your last chance to save 20% on our menu

Another tip – go easy on the adjectives. Many marketers are tempted to pile on superlatives in an effort to sell the message. But adjectives can be perceived by the savvy consumer to be nothing more than promotional fluff. Our advice: don't go overboard. A meaningful piece of information is always better than an empty adjective. Even better, use a meaningful adjective – ‘free' is an obviously potent one (and more spam-filter friendly these days, particularly if the subscriber's email address is familiar with the sender's).

2. Descriptiveness

It's generally deemed best practice to set clear expectations about your email in the subject line. I'd agree to a certain point. As with click-baiting headlines, misleading subject lines should be banished to the spam folder. You could have the most enticing subject line ever, but if it isn't wholly relevant to the contents of your email you'll risk losing readers and therefore click-through rate.

However, there's nothing wrong with an intriguing subject line; and you certainly don't want to be so prosaic that your email fades into obscurity. Be direct enough to target those likely to be interested in your offering, while creating enough intrigue to stand out in your recipient's inbox.

In an A/B test, the more intriguing subject line below notched up a none too shabby 41% open rate and 40% click-to-open rate; while the descriptive version demonstrated the self-fulfilling nature of a direct approach – those who're interested in the what's being offered upfront will therefore be more likely to click through – with a lower open rate (39%) but a slightly higher (43%) click-to-open.

[A] Do you deserve a weekend treat? We think so.
[B] Two mains, pudding & wine for under £30

3. Relevance

Knowing what kind of words will resonate with individual recipients is impossible, but you may have resources to at least help you map a subject line to the things that motivate them as a group. Can you glean any insight from subscriber data, customer profiling or purchasing behaviour?

If you're tailoring a subject line to a specific segment of your database, choose words with that audience in mind. In the subject line below, ‘claim' may be perceived to be promotional and a touch clinical sounding.

Remember to claim your free ice-cream voucher

Then again, it speaks to value-seeking subscribers who're already engaged with the sender and are expecting voucher offers. It's more powerful than ‘Have you enjoyed your free ice-cream voucher?' as it infers that something is due to the recipient, still to be enjoyed. Like other powerful verbs, ‘claim' expresses immediacy and tells the recipient we want them to do something.

This simple, single-minded subject line below sells an experience rather than just the promotion. There's a sense of exclusivity about it as the offer is being presented as personal to the recipients, who are made to feel valued.

A special offer for steak lovers

Whatever language you use, make sure it's in line with your brand tone of voice for continuity. Loyal subscribers may switch off from a subject line than doesn't sound like the company they know and like, or with which they've formed an emotional connection.

Also, be intuitive. Don't tell subscribers what they already know – a classic example is repeating the sender name, i.e. your brand or outlet, in the subject line. Instead use the precious space you have to entice them.

4. Timeliness

Timeliness goes hand in hand with relevance. Think about the words you're using in the context of the dispatch time – time of day, day of week, seasonality. If there's a timely or topical hook that's relevant and might strengthen your message, use it.

The examples below were responsive to how a major world event unfolded, giving the subject lines of-the-moment context and therefore increased relevance.

5. Length and position

So your subject line isn't cut off in mobile browsers, aim for a maximum of 40 characters (we count about 35 characters on an iPhone). If it needs to be longer, prioritise – or ‘front-load' – the most salient part of the message, such as a price-point. Plus remember you have the summary line, or pre-header, as it's also known, to supplement the subject line.

While conciseness can make for a punchy subject line, don't be fooled into thinking less is always more. Balance brevity with detail for the best result. We find that the stronger the offer, the more economic with words you can afford to be.

6. Originality

Continuity of message is a positive thing, but don't let your subject lines become predictable. Keep subscribers interested in your email comms by surprising, titillating and amusing them. Deploy witty wordplay or provocative openers, get creative with punctuation, add a poetic flourish – or simply vary your language. As you'd expect, mixing it up can give open rates a healthy boost.

Don't just try things for the sake of being different, though. Stick closely to your strategy and opt for the tactics that will help you best engage your audience in the message you're communicating.

Here are a few examples of ‘original', eye-catching subject lines we've seen recently:

You. Clothes off. Now. – Innocent Smoothies (naked film initiative)
Wrap. Eat. Sleep. Repeat. – Wagamama (new dish)
Eau my gold, it's here – Debenhams (new perfume)
Everyone else is doing it. Why aren't you? – Ocado (introductory offer)
We'll pay you to sleep with us – Mr & Mrs Smith (hotel offer)

Try to avoid upper casing, exclamation marks and characters in place of real tone of voice. There should always be a strategic reason for applying stylistic features – like the tactical use of emojis to highlight a specific feature or benefit, or to illustrate a word for a more succinct, visual message.

You could try running your creations through a subject-line performance tool, like Touchstone, which also suggests words to use. Though we're not sure of the scientific integrity of these things, particularly given the absence of campaign context.

With email, it's important to understand that everything is relative. To every tactic you apply there's an influencing factor. For instance, varying your approach, i.e. whether being more original with your language or going for a more intriguing and less descriptive subject line, may elicit response from a completely different group of subscribers within your database, including those who've been inactive. And if you deviate from your usual style of line, you may see a drop in response from your regular openers.

While comparative testing isn't watertight, knowing what you want to achieve and continual experimentation is important to simply seeing what works – regardless of how exactly – and to keeping content fresh.

If you're looking to sharpen up your email performance, get in touch with our expert team.