How to write email subject lines

It’ll come as no surprise to you, I imagine, that the word “free” in an email subject line doesn’t convert all that well. I mean, yecch, right? Cheesy lures are gross. But I briefly lost my eyebrows in my hairline when the same data (from Mailchimp, which knows this stuff*) suggested that the word “freebie” works beautifully. Who knew?

So, I did what all writers do when confronted with unexpected facts: I dug. And now you don’t have to. I’ll tell you what you need to know when it comes to subject-line semantics — specifically, what doesn’t work (rock-bottom) and what works well (rock‑star).

First, the building blocks:


A typical inbox reveals about 60 characters of an email’s subject line, while a mobile phone shows just 25 to 30 characters, says HubSpot — and 46% of all emails are opened on mobile devices. So, you should get to the point in 6–8 words.


If the optimal range is 6–8 words, use them all — most of the time. Now and then, a one-word subject line, if it’s really powerful (i.e. not “Meeting” but “Gobsmacked”), can pay off but in general aim for this kind of scope:

• Requesting Project X idea submissions — due 15 Jan
• Employee Survey: Please complete by EOD Friday
• Meet about social media strategy Tuesday?
• An introduction: Nelly P, meet Daniel J
• Potential collaboration on radio commercial strat
• John, see how you compare with your competitors


Since you don’t know how much of the subject line will be viewable from the reader’s phone, put the most important information at the beginning. Otherwise, compelling details could get chopped off. Take another look at the previous list of examples.


If you’ve been referred by a mutual acquaintance, don’t save that for the body of the email. Put the full name in the subject line, to grab the reader’s attention:

• Referred by Thuli M for project pitch opportunity


In your follow-up email subject lines, be sure to reference your past meeting or conversation. This helps your recipient to remember who you are.

• Met at Motherland Dunkeld yesterday: job application attached

Second person

“You” and “your” work beautifully, because they appeal to the reader’s ego. The reader’s own name is also a rock-star inclusion, if personalisation is possible.

Numbers & lists

Many of the variables that make up a good blog post title also make a good email subject line. Numbers attract attention because our brains are drawn to digits, because lists are easier to process, and because stats and facts create curiosity.

3 reasons most content marketing absolutely sucks

Now to the surprising stuff:

Free vs freebie

Does including “free” in your subject line entice readers to open your message? It does but not always, not on average. However, use of the rock-star word “freebie” results in a much larger increase in open rates.

Urgent & breaking

Let’s say you need to communicate urgency, using attention-grabbing words to let your readers know that your email requires immediate attention. Words like “urgent” and “breaking” get higher open rates. “Alert” doesn’t work all that well. “Reminder” actually tanks completely, and “announcement” and “invitation”? Rock‑stars.

Two-word phrases

“Thank you” and “sneak peek” work well; “sign up”, “buy now” and “last chance” are rock-bottom — which is a pity, since the whole bloody world uses them.

Title case

This one bamboozles me: the impact of capitalisation on open rates. Now, I expected that the use of an entirely capitalised subject line would yield lower open rates than a sentence-case one. And it does. Because… IT’S SHOUTING!

But lookie here: Title case, where The First Letter of Each Main Word is Capitalised, works better than sentence case: Where the first word starts with a capital letter.

I dunno. Didn’t see that one coming.

Onward to the randoms:

Shock, horror

Rude words are a turnoff, unless you apply them to yourself. “I’m a fool” does well, while “Fools” on its own can come across as abrasive.

What not to do

Rules are also a turnoff, in the abstract. “1 dumb business rule you should ignore all day”, which is specific, does better than “Rules for business” on its own, which feels stern, abstract and not personal or intriguing enough.

Raise your glass

Tributes work well, says Talking Shrimp (2020), as in This is for [UNEXPECTED GROUP OR THING] or Long live [UNEXPECTED GROUP OR THING]:

• A toast to the serial cart‑abandoners
• An ode to the banana clip
• I salute you, Spinning Rainbow Ball of Doom

Skelm secrets

So do unexpected lessons and personal stories (Talking Shrimp again), as in The [SUBJECT] they all kept from you, or [NUMBER] [CATEGORY] lessons from [UNEXPECTED FIGURE], or Why we turned down [HUGELY DESIRABLE THING]:

• The biggest investment risk you’ve never heard of…
• The genius website plugin you definitely don’t know about

• 9 language lessons from The Donald
• Remind us not to befriend the chatty stranger on LinkedIn…

Honest admissions

And, in my experience, the personal/self-effacing confession is pure rock‑star:

• My husband hated my last newsletter
• There’s something awkward I need to admit to.
• Last week, a client made me ugly‑cry.

So, off you go then. Now you know.

  • Mailchimp studied 24bn delivered emails with subject lines composed of 22 000 distinct words. If you think that sounds like a lot of data, you’re right.

A version of this article originally appeared in Tiffany Markman’s MarkLives column.

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