Measuring the success of your email subject line can be more straightforward compared to other email metrics. In most cases an open = a win. But that doesn’t mean that writing effective, clever, and persuasive subject lines is easy (it’s not).

Subject lines force you to write in an active, succinct, and creative way. And for this reason, those one-liners can be one of the more challenging email elements to master. So whether writing subject lines psychs you up or out, I want to share some subject line dos and don’ts to help you with your next campaign.

Then, this post will walk through how you can incorporate these best practices into your subject line writing process.

Do: keep it short (around 3 words)

Here at SendGrid, we’ve analyzed emails sent through our system and our subject line data reveals that recipients prefer and will be more likely to open a subject line when it’s three words. Does that mean if you think you have the perfect subject line at 4 words you should change it around completely? No—guidelines and trends are just that—they are not universal law.

Still finding yourself in a writer’s block? Consider putting a spin on puns or easily recognizable phrases. Although these phrases are trite and lazy on their own, when you alter or put a personal spin on a pun applicable to your brand or service, you usually catch people’s attention because they were expecting to read something else.

The following subject line from a smoothie delivery company  that puts a twist on the phrase, “no way Jose.”

RE: Yes Way Frose!

The accompanying email included cocktail recipes that you could make with their smoothies—one of which is a rose smoothie(!)

Yass way, I am opening that email.

Do: Write the subject line last

You may have an idea for your subject line when you’re pulling together an email campaign. But until you’ve selected all copy pieces and written accompanying snippets and headlines, you won’t have the full picture of what you’re really trying to explain. And as a result, distilling your content into one line of text will prove quite challenging.

There are of course exceptions to this tip. Sometimes, a flash of brilliance occurs and the subject line almost writes itself before finishing other steps. For cases when that doesn’t happen, wait until you have finalized every other piece of content before attacking the headline or subject line.

Do: make it specific and urgent

Think of the subject line as your first CTA or touch point with your recipient. If you don’t draw them in right away, you’ve lost them. And while humor and wit are usually rewarded, keep in mind that you need to give your recipient some sort of (accurate) taste of what’s inside.

To achieve this, try to use action verbs that resonate with your audience as much as possible. Verbs are a writer’s best friend because they help you do more with less—something that will always play in your favor.

I recently received an email from Strava that draws on the inherently competitive nature of Strava users and uses an appropriate verb in its subject line:

How Fast Can You Run A Mile?



Although I didn’t partake in the mile challenge, I read all about the campaign and went to the app afterward to see what my riding and running buddies were up to. That’s a win for Strava right there.

Do: Experiment

No single (legal) email list is the same, which means that you won’t know how your audience will react to your subject lines until you actually send them something. Fortunately, subject lines happen to be some of the simplest email components to test.

Consider sending two or more subject lines to different segments of your email list. One subject line may be a bold subject line that pushes the envelope while the other could be a more traditional and literal subject line. The options are endless. For more on how to test and experiment in your own campaigns read up on some common questions and answers to A/B testing.

Don’t: Overdo it with !!!!, ALL CAPS, and other frills

We’re all likely guilty of adding in explanation points or being tempted to WRITE IN ALL CAPS TO GET OUR POINT ACROSS. We use these language tools to help us emphasize, but often these tactics lose or agitate the recipient.

Tread extra lightly when considering hitting your caps lock or using excessive exclamation points or other symbols.

Allow your subscribers to react to the meat of your copy instead of the frills.

One modern exception to this rule, depending on your industry, is using emojis. For some campaigns (such as marketing to millennials) it can work great. For others, it falls flat. See the previous tip about testing to find the right balance for your own email program. Emojis also allow you to use fewer characters, so if it’s working for your engagement, then go for it.

Do: Have fun

Finally, don’t forget that writing subject lines can be fun and a great place to explore/try new things with your writing style. Subject lines are short, but mighty nuggets of content that set the pace for all following email engagement events. So take your time, give the subject line some thought, and follow the tips above (but know what works best for you).

For more email marketing best practices beyond the subject line, check out our A-Z Email Marketing Guide which covers everything from subject lines, to email frequency, testing schedules, and more.

As a senior content marketing manager at SendGrid, Kelsey oversees the SendGrid Delivery blog. Her downtime is dominated by either her mountain bike or skis (depending on current weather forecast)–and mixing up a salty marg afterward.