Every email is two messages. The body is the one you wrote. The subject line is the one that decides whether the body gets read, and most writers spend ninety seconds on the body for every two seconds on the subject.
The constraint is brutal. A phone shows roughly 35 to 45 characters of a subject line before truncating. That is shorter than a tweet and shorter than most single sentences. Whatever you want the reader to do has to survive that window.
The subject line's real job
A subject line is not a summary. It is a reason to open, plus enough context that the reader knows what they are opening. Those are two different jobs and both matter.
A line that only summarises — "Meeting notes" — gives the reader no reason to open now. A line that only teases — "Quick question" — gives them no idea what is inside and gets ignored. The best lines do both in the first few words.
A useful formula: the specific thing plus the action or the deadline.
Budget review: two figures need your sign-off by Thursday
The reader knows the topic, knows what is needed, and knows when. Nothing is hidden and nothing is wasted.
Front-load the meaning
Because of truncation, the first three words carry most of the weight. Put the specific noun there, not the pleasantry.
Weak: Following up on our conversation about the vendor contract Strong: Vendor contract: one clause left to agree
The weak version spends its visible characters on "Following up on our," which tells the reader nothing. The strong version uses the noun the reader will recognise and puts the decision point second.
Test every subject line by cutting it after 40 characters. If the visible part still tells the reader what the email is about, it is well built.
Say what you want
The most common failure in workplace email is a subject line that describes the topic but not the request.
Project update
What does the sender want? Nothing? Something? The reader has to open the email to find out, and if they are busy, they will open it later, which means never.
Project update: need your approval on the timeline
Now the subject line carries the ask. The reader can triage without opening, which is the entire point of a subject line in a busy inbox.
Some useful verbs to front-load: "approve," "confirm," "review," "decide," "sign," "send," "reply by." Each one tells the reader what will be required of them.
Deadlines belong in the subject
If the email has a deadline, the deadline should be visible before truncation or immediately after. "By Friday" in the subject line saves a round trip, because the reader knows the urgency without opening the message.
Invoice 2201: payment due 14 November Draft agenda: comments by Tuesday noon
Put the date in a form that cannot be misread. "Tuesday" is clearer than "tomorrow," and "14 November" is clearer than "14/11" for any reader outside your country.
The reply problem
When you reply to an email, the subject line is inherited: "Re: Vendor contract: one clause left to agree." This is usually fine, because the reader already has context. But when a thread changes topic, the inherited subject lies.
The practical rule: keep the subject when the conversation continues, change it when the topic changes. If a thread about a contract turns into a thread about hiring, start a new email with a new subject line. Threads that drift become impossible to find later, and search is how most people retrieve email.
For long threads, it also helps to restate the ask in the first line of the body. The reader may be opening the twelfth message, and the subject line has been the same since the first.
What to avoid
All caps. It reads as shouting, and spam filters treat it with suspicion. Use the case converter if you inherited a shouted subject from somewhere else.
False urgency. "URGENT" on a routine request trains readers to ignore the word. Reserve it for actual urgency, and it will keep working.
Emoji. A single relevant emoji can help in informal contexts. Three emoji in a subject line reads as marketing, and in most workplaces it reads as a mistake.
Empty subjects. Never send one. A blank subject is a promise that the email does not matter.
The internal reference. "RE: Q3 planning doc v4 FINAL final" tells the reader about your file-naming, not about the work. Say what the email needs.
Subject lines for different jobs
The same principles produce different shapes for different emails.
The request. "Review the one-page brief by Wednesday" — noun, verb, deadline.
The update. "Launch moved to 12 November: what changes for you" — the fact, then the consequence.
The introduction. "Intro: Sam Okafor (design) and Priya Raman (engineering)" — who, and why they are meeting.
The apology or correction. "Correction: the figures in yesterday's report" — name the problem plainly; euphemism makes it worse.
The cold outreach. "Question about the Leeds warehouse lease" — specificity is the only thing that separates you from spam.
In each case the pattern is the same: the specific thing first, the action or consequence second, and nothing that could be cut without losing meaning.
A thirty-second habit
Before sending, read the subject line as if you were the recipient scanning fifty emails. Ask three questions: do I know what this is, do I know what it wants, and do I know when it wants it?
If any answer is no, rewrite the line. It costs half a minute and it is the difference between an email that gets answered and one that gets buried.
The body of the email is where you do the work. The subject line is where you make sure the work gets seen.