The subject line is the first thing a reader sees, and often the only thing. In a business email it has one job: to tell the reader honestly what the email is about, so they can decide whether to open it now, later or not at all. Read the short guide below, then press Start exercise for three tasks: sort subject lines, name the problem behind each bad one, and answer a quiz. The rewrite tasks at the end are for your notebook or a class discussion.
What a good subject line does
It is honest. The email delivers what the subject line promises.
It is about the reader's world: their company, their project, their town, their role. "Bookkeeping for your new farm shop" beats "Proseware bookkeeping services".
It is short, with the important words first. Many phone mail apps show only the first 30 to 40 characters or so. The exact number depends on the app, the screen and the font size, so treat this as a rough illustration, not a rule.
It looks like a person wrote it. Normal capital letters, no row of exclamation marks, no "FREE".
Four kinds of subject lines
Kind | What it does | Example |
|---|---|---|
Clear and relevant | Names the topic and why it matters to the reader | Forklift checks for your new Leeds warehouse |
Clickbait | Teases or exaggerates to get a click, and hides what the email is about | You won't believe what we found on your website |
Spammy | Looks like mass advertising: capitals, "FREE", !!!, a deadline | FREE AUDIT!!! Limited spots, act now |
Vague | Says nothing, so the reader has no reason to open it | Quick question |
Clickbait and spammy subject lines often overlap. Both try to get the email opened without telling the truth about it.
What the reader sees on a phone
Here is how a long subject line can look in a narrow inbox. The cut-off point is an illustration.
Subject line as written | What the reader may see |
|---|---|
Proseware bookkeeping services for wineries, breweries and farm shops | Proseware bookkeeping services for wi... |
Bookkeeping for your new farm shop | Bookkeeping for your new farm shop |
Many inboxes also show preview text under or next to the subject: the first words of the email body. Subject and preview work as a pair, so the first sentence should not repeat the subject or waste the space on "I hope this email finds you well".
Why a misleading subject line is a trust and a legal problem
Trust. When a subject line promises something the email does not deliver, the reader feels tricked. "Re: our call yesterday" from a stranger, or "Your invoice" on an advert, gets opened once, then deleted and often reported as spam. Spam reports make it harder for the sender's future emails to reach anyone (see sender reputation and warm-up). And the reader remembers the company name for the wrong reason.
Law. An overview, not legal advice:
United States. The FTC's CAN-SPAM compliance guide says: "Don't use deceptive subject lines. The subject line must accurately reflect the content of the message." The From, To and Reply-To lines must not mislead either. The guide also says "the law makes no exception for business-to-business email", and each email that breaks the rules can lead to a penalty.
Germany. § 6 (2) of the Digitale-Dienste-Gesetz (DDG) says that in a commercial email neither the sender nor the commercial nature of the message may be concealed or disguised in the header or the subject line. Separately, § 7 UWG generally requires the recipient's prior consent for advertising by email at all, also when the recipient is a business.
Other countries have their own rules. The cold email and the law lesson compares them.
Rewrite tasks
Write a better subject line for each email. Each one is the first email to someone who has never heard from the sender. Then compare with the model answers.
Proseware (bookkeeping) writes to the office manager of Coho Winery, which has just started selling wine online. Old subject: "Hello from Proseware".
Contoso (IT services) writes to Alpine Ski House, which hires about 40 seasonal ski instructors every December. Old subject: "LAST CHANCE: IT support 30% off!!!"
Fourth Coffee (office coffee service) writes to Trey Research, which moved into a new building in October. Old subject: "Re: coffee".
Fabrikam (forklift service) writes to the warehouse manager of Wingtip Toys. Old subject: "Fabrikam, your trusted partner for innovative intralogistics solutions since 1998".
Margie's Travel writes to the operations manager of Lamna Healthcare, whose care coordinators travel between three offices. Old subject: "Quick question".
Model answers
Other answers can be just as good. Check yours against three questions: is it honest, is it about the reader, are the key words at the start?
Bookkeeping for your new online shop. About the reader's news, not about the sender.
Laptops ready for your December instructors. No discount, no capitals, no deadline. The season is the reason to write now.
Coffee for your new building. The "Re:" goes: there was no earlier email.
Forklift servicing at Wingtip Toys. The old line was all about the sender and far too long for a phone.
Travel between your three offices. "Quick question" says nothing. If the email really is one question, the subject can name its topic.
Teacher notes
How to run it (30 minutes). 5 minutes: read the guide together and look at your own inbox (or a projected sample of invented emails). Which subject lines made you open something, and which made you delete it? 15 minutes: the three tasks in the exercise. 10 minutes: the rewrite tasks in pairs; each pair reads out its best line and the class checks it against the three questions in the model answers.
Common mistakes.
Treating "Quick question" as clear. It is short, but it tells the reader nothing about the topic.
Thinking a misleading subject line is fine if the email itself is honest. The deception happens before the email is opened.
Confusing a real "Re:" with a fake one. Replying in an existing thread is honest; putting "Re:" on a first email is not.
Making subject lines clever instead of clear. A pun the reader has to work out is a small piece of clickbait.
Follow-up questions.
Why do some senders use fake urgency even though it annoys readers? Who pays the price later?
The FTC guide speaks about subject lines; the German DDG speaks about hiding the sender and the commercial nature. What do the two rules have in common?
How could a company test which of two honest subject lines works better? (See the A/B test lesson.)
For business English classes. Collect the useful patterns: "[Topic] for your [situation]", "Question about [specific thing]", "[Topic] at [company]". Both sentence case ("Coffee for your new building") and title case ("Coffee for Your New Building") are used in English; sentence case looks more like a personal message.