How to Write Better Emails: The 9-Second Rule

The answer to how to write better emails is brutally simple: write less, structure more, and make the action obvious. Microsoft Research measured this on 938,035 real corporate messages for SIGIR 2017 and found that reply rate peaks at around 40 words, then falls away steadily. By 500 words, a message is roughly three times less likely to be answered than a 40-word one. The problem is that almost nobody writes emails that short.

Here is the uncomfortable truth most email advice dances around: your recipients do not care about your email. They care about their own inbox. According to Litmus’s email engagement research, the average person spends just nine seconds reading an email before deciding to act, skim, or delete. Nine seconds. That is not a reading experience. It is a triage decision. And if your email does not survive that triage, it does not matter how good the content was.

This is what drives the philosophy behind Swizero: email is not a reading problem, it is a volume problem. Every inbox is a stream of demands competing for a finite resource: your attention. The emails that win are the ones structured for how people actually process information, not the ones that took the longest to compose.

Why Do Most Emails Get Ignored?#

Most emails get ignored because they violate a basic rule of human attention: people scan before they read. When someone opens your message and sees a wall of text with no clear purpose, the cognitive cost of parsing it outweighs the perceived value. So they close it, flag it for “later,” and later never comes.

Josh Bernoff, former Forrester Research analyst and author of Writing Without Bullshit, calls this the Iron Imperative:

Treat the reader’s time as more valuable than your own.

— Josh Bernoff, Writing Without Bullshit

A hastily composed email becomes what Bernoff describes as a “puzzler”: the recipient reads it and asks, “Why did I get this? What am I supposed to do about it?” That confusion is where emails go to die.

The data backs this up. Litmus’s 2022 email engagement study found that 30% of all emails are looked at for less than two seconds. Another 41% get between two and eight seconds. Only 29% of emails receive what researchers classify as a genuine “read” (more than eight seconds of attention).

Those numbers should change how you think about writing. You are not composing a document. You are designing a nine-second experience.

The Five Rules of Emails That Get Read#

Not all of these will surprise you. A few might. The research behind them is what matters.

1. Keep it between 50 and 125 words#

The Microsoft Research study of the Avocado enterprise email collection plotted reply rate against body length across 938,035 real corporate messages and found an inverted U. Reply rate climbs from 4.65% at one word to 9.64% at around 40 words, then falls steadily to 2.82% by the time a message reaches 500 words. Median reply time gets worse the entire way up.

Read that curve carefully, because it says two things. Emails that are too short get ignored, since a bare sentence with no context is easy to defer. And every paragraph past a few dozen words costs you replies. The 500-word email is not merely slower to answer. It is roughly three times less likely to be answered at all.

The arithmetic agrees. Adults read English non-fiction at roughly 238 words per minute, according to Marc Brysbaert’s meta-analysis of 190 reading studies in the Journal of Memory and Language. So 50 words takes about 13 seconds and 125 words takes about 32 seconds. Litmus puts the median email at nine seconds of attention, and Microsoft’s 2025 Work Trend Index says most of the 117 emails a worker receives daily are skimmed in under a minute. A 125-word email is already asking for three times the median attention span. A 500-word email is asking for a favor.

2. Write at a simple reading level#

This sounds patronizing. It is also the change with the most direct experimental backing. Daniel Oppenheimer’s Consequences of Erudite Vernacular Utilized Irrespective of Necessity, published in Applied Cognitive Psychology in 2006, took the same essays and swapped plain words for complex ones. Readers rated the complex versions as coming from less intelligent authors, and the effect was driven by processing fluency: text that is harder to decode makes the writer look worse, not smarter.

Simple does not mean dumbed down. It means short sentences, common words, and active voice. It means writing “Can you send the file by Friday?” instead of “It would be appreciated if you could facilitate the transmission of the relevant documentation at your earliest convenience.”

Honestly, this was the hardest rule for me to internalize. Writing simply feels reductive when you are discussing complex topics. But reading level is not about intelligence; it is about processing speed. Simple language gets processed faster, which means your point lands in those nine seconds instead of getting lost.

3. Front-load the action#

Put what you need from the reader in the first two sentences. Not the third paragraph. Not after the context. The ask comes first, and then the reasoning.

The same Microsoft Research analysis separated emails that contain an explicit request from those that do not. Messages with a request drew a 14.81% reply rate. Messages without one drew 7.45%. Asking clearly roughly doubles your odds, which is a larger effect than anything you will get from tone, timing, or word choice.

Most people write emails like essays: background, analysis, conclusion. But your reader is not grading your paper. They are scanning on a phone between meetings. If the action is buried, it is invisible.

Cal Newport, Georgetown computer science professor and author of A World Without Email, argues that a single well-structured message with a clear ask eliminates the cascade of follow-up replies that poorly written emails generate. His research on email protocols calls this “process-centric email”: front-loading every piece of information the recipient needs so the exchange resolves in one message instead of five.

4. Use a subject line under 7 words#

Marketo’s analysis of 2.4 million emails found the sweet spot for subject line engagement was 41 characters, roughly 7 words. That is about 10 characters shorter than the average subject line.

Mobile inboxes display only 33-43 characters of a subject line. If your key information does not appear in that window, it does not exist for mobile readers. And the majority of emails are now opened on mobile.

The best subject lines are specific and complete. “Q3 budget: need your approval by Thursday” works. “Quick question” does not, because it gives the recipient no reason to prioritize opening it.

5. One email, one topic#

This is the rule everyone knows and nobody follows. If your email covers three different topics, you have sent three emails wearing a trenchcoat. The recipient will respond to whichever topic is easiest, ignore the rest, and you will end up sending follow-ups anyway.

Splitting topics across separate emails also makes things searchable later. Trying to find that one budget decision buried in a thread about the holiday party schedule is a special kind of frustration that costs knowledge workers real time every week.

What Does an Effective Email Actually Look Like?#

Seeing the principles in practice is more useful than reading about them in the abstract. Here is a real comparison.

Before (147 words, college reading level):

Hi team, I wanted to reach out regarding the upcoming client presentation that we have scheduled for next Thursday. I’ve been reviewing the latest metrics and I think there are some important considerations we should discuss before finalizing the deck. Specifically, the conversion data from Q1 shows some interesting trends that might impact how we frame our recommendations. I was wondering if everyone could take a look at the attached spreadsheet and let me know their thoughts. Also, I think we should probably schedule a prep meeting sometime early next week. Let me know what times work for you. Thanks!

After (52 words, third-grade reading level):

The client presentation is Thursday. Two things I need:

1. Review the attached Q1 conversion data by Monday
2. Pick a prep meeting time [Calendly link]

The Q1 trends change our recommendations — I flagged the key rows in yellow. Takes 5 minutes to review.

Same information. Half the words. The action is in the first two lines. The busy reader knows exactly what to do and how long it will take.

How Can You Write Better Emails Faster?#

The irony of email writing advice is that it asks you to spend more time thinking about something you already spend too much time doing. According to the Radicati Group’s Email Statistics Report, 2024-2028, knowledge workers send and receive an average of 121 business emails per day. Writing each one with careful structure and a third-grade reading level is a real ask.

This is where the craft meets the constraint. If your inbox has no boundary (no fixed limit on what demands your attention) then every email you write is competing against an infinite stream of incoming messages. You cannot write thoughtfully when you are also triaging constantly. The two modes are incompatible, and the result is decision fatigue that compounds through your day.

I could write a whole post about why unconstrained inboxes make it impossible to communicate well, but the key point here is this: the cognitive load of unprocessed emails degrades your ability to compose clear messages. You write worse when your inbox is overwhelming you. It is a feedback loop.

Swizero’s approach (reducing your inbox to a fixed card limit) is designed to break that loop. When you are working through a handful of cards instead of scrolling an endless list, you have the mental bandwidth to write with intention. And for the messages where you just need to reply quickly, Swizero’s AI drafting applies the research-backed principles automatically: short sentences, clear asks, appropriate reading level.

The Subject Line Is Half the Battle#

Subject lines deserve their own section because they are where most emails succeed or fail before the body is ever read. Marketo’s study of 2.4 million emails confirmed that 7 words is the engagement sweet spot, but length is only part of the equation.

Effective subject lines share three qualities:

• Specific: “Budget approval needed by Friday” beats “Quick question”
• Complete: The reader should understand the email’s purpose without opening it
• Scannable: No clever wordplay, no buried lede; say what the email is about

One caveat worth mentioning: most subject line research comes from marketing emails, not workplace communication. The dynamics are different. Your coworker’s email is going to get opened regardless of the subject line, but a clear subject line still determines whether it gets opened now or gets buried under 30 newer messages; subject lines are a prioritization signal, not just an open-rate lever.

The Hidden Cost of Unclear Emails#

Every unclear email you send generates at least one clarifying reply. Often two or three. Microsoft Research’s SIGIR 2017 study of enterprise email found that content properties, including the length of the subject line and the length of the body, are among the signals that predict whether a message gets answered at all and how long it takes. Poorly structured emails do not just fail once. They spawn the reply chains that multiply the total time spent on what should have been a single exchange.

Adam Grant, Wharton organizational psychologist and author of Think Again, describes the compounding cost of unclear communication. People check email 74 times a day and switch tasks every 10 minutes, creating what Grant calls “time confetti”:

Time confetti is an enemy of both energy and of excellence. If we want to find flow, we need better boundaries.

— Adam Grant

Every unclear email you send adds to someone else’s time confetti, generating clarifying replies, context switches, and tiny taxes on everyone’s focus. Even within the constraints of email, writing clearly is the strongest defense against this spiral.

Here is a useful test: before you send, ask yourself whether the recipient could forward your email to someone else and that person would understand what is needed without any additional context. If the answer is no, you have not finished writing.

The investment is small. An extra 30 seconds of editing before sending saves minutes (sometimes hours) of follow-up. That math compounds across the dozens of emails you send every day.

Frequently Asked Questions#

How long should a professional email be?#

Aim for 50 to 125 words. Microsoft Research’s analysis of 938,035 enterprise emails found reply rate peaking at about 40 words (9.64%) and falling to 2.82% by 500 words. At the average adult non-fiction reading rate of 238 words per minute, 50 to 125 words is 13 to 32 seconds of attention, already generous next to the roughly nine seconds Litmus measures for the average email.

What is the best subject line length for email?#

According to Marketo’s study of 2.4 million emails, 7 words (approximately 41 characters) is the sweet spot for engagement. On mobile, only the first 33-43 characters display, so front-load the most important information.

Does email reading level really matter?#

Yes, and not in the direction most people assume. In Daniel Oppenheimer’s 2006 experiments in Applied Cognitive Psychology, swapping simple words for needlessly complex ones made the same text read as the work of a less intelligent author. The effect was driven by processing fluency: harder-to-read text costs the reader effort, and the reader charges that cost back to you. Simple language is not about dumbing down; it is about reducing the effort required to understand and act on your message.

How much time do people spend reading an email?#

Litmus email engagement data shows the average has dropped to approximately 9 seconds per email as of 2022, down from 13.4 seconds in 2018. Thirty percent of emails receive less than 2 seconds of attention.

Can AI help write better emails?#

AI drafting tools can apply research-backed email writing principles (appropriate length, clear structure, simple reading level) automatically. Swizero’s AI drafting feature generates concise, action-oriented replies based on these best practices, so you do not have to consciously apply every rule for every message. If you are curious about the mechanics, here is how AI email assistants actually work.

Sources#

1. How Many Words Do We Read Per Minute? A Review and Meta-Analysis of Reading Rate. Marc Brysbaert, Journal of Memory and Language, vol. 109, 2019. Meta-analysis of 190 studies and 18,573 participants: average silent reading rate of 238 words per minute for English non-fiction.
2. Email Attention Spans Increasing. Litmus. Average email reading time declined from 13.4 seconds (2018) to 9 seconds (2022); 30% of emails get under 2 seconds.
3. How to Optimize Your Email Subject Line Length. Campaign Monitor / Marketo. Analysis of 2.4 million emails found 41 characters (7 words) is the engagement sweet spot.
4. Email Statistics Report, 2024-2028. The Radicati Group, 2024. Knowledge workers send and receive 121 business emails per day on average.
5. Deep Habits: Write Your Own E-mail Protocols. Cal Newport, Georgetown University. Framework for reducing email back-and-forth through structured communication.
6. Writing Without Bullshit. Josh Bernoff, 2016. The Iron Imperative: treat the reader’s time as more valuable than your own.
7. How to Stop Languishing and Start Finding Flow. Adam Grant, Wharton. “Time confetti” concept: constant email checking fragments attention and degrades work quality.
8. Consequences of Erudite Vernacular Utilized Irrespective of Necessity: Problems With Using Long Words Needlessly. Daniel M. Oppenheimer, Applied Cognitive Psychology, 20(2), 139-156, 2006. Needlessly complex vocabulary lowers judged intelligence of the author, mediated by processing fluency.
9. Characterizing and Predicting Enterprise Email Reply Behavior. Yang, Dumais, Bennett & Awadallah, SIGIR 2017, Microsoft Research. Analysis of the 938,035-message Avocado enterprise email collection: reply rate rises from 4.65% at one word to 9.64% at ~40 words, then falls to 2.82% at 500 words; emails containing an explicit request reply at 14.81% versus 7.45% without.
10. Breaking Down the Infinite Workday. Microsoft Work Trend Index, 2025. Average worker receives 117 emails per day, most skimmed in under a minute.