Email Subject Lines: 40 Examples, Length Tips and How to Test

Your subject line decides whether the email gets opened, ignored or reported. It has a few words and one job: make the right person want to read on. Most advice on the topic is a list of tricks. This guide is different: it explains how subject lines are actually displayed, what makes them work, gives forty examples sorted by purpose, tells you what to avoid and shows how to test your own. Use the examples as starting points, not as templates to copy, because the best subject line is the one that sounds like your brand talking to your customer.

What a subject line does

The subject line is the single line of text in the inbox list, shown next to your sender name and a short preview of the body. Together these three elements make up the first impression. People rarely read the line closely. They scan it in a fraction of a second and decide, based on whether the sender is familiar, whether the line is specific and whether it seems relevant right now. Because it works with the sender name and preview text, you should design all three together.

How long should a subject line be?

There is no magic number, because display depends on the device, the email app and the screen width. A phone often shows somewhere around 30 to 45 characters of a subject before cutting it off, while a desktop client may show 60 or more. The practical rule is to put the most important words first, so even a truncated line makes sense. Anything beyond about 50 characters is a risk. Do not count characters obsessively. Read the line on your own phone and see where it breaks.

Principles that make subject lines work

• Be specific. “Your order FX-20481 has shipped” beats “An update for you”. Details signal that the message is for this person.
• Match the promise. If the subject says one thing and the body another, people stop trusting you, and complaint rates rise.
• Lead with the benefit or the news. What changes for the reader, not what you did.
• Sound like a person. Plain, conversational language usually outperforms headline-style writing.
• Create curiosity honestly. A question or a partial reveal can work, but only if the email delivers.
• Add urgency only when it is true. A real deadline helps. A fake countdown every week teaches people to ignore you.

40 subject line examples by purpose

Edit these to fit your brand and audience. Each pairs a purpose with a pattern.

What to avoid

• Deceptive lines. Faking a reply (“Re: your request”) when there was none is misleading and in many places unlawful.
• All capitals and heavy punctuation. They look like spam to people and filters.
• A wall of emoji. One can help a line stand out. Several look noisy, and some render badly on older devices.
• Vague teasers. “You will not believe this” says nothing.
• Sameness. If every email starts with the same phrase, people stop seeing it.

Spam filters look at many signals together, so a single word rarely matters, but a pattern of pushy language combined with poor authentication and low engagement does. Fix the basics first: see our guides to email deliverability and SPF, DKIM and DMARC.

Personalising subject lines

Using a name can help, but it is the weakest kind of personalization and loses effect when overused. Stronger options use behaviour or context: the product someone viewed, the date of their appointment, their city, or what they bought last time. In Flowfox you can insert these with Liquid, for example {{ contact.first_name | default: "there" }}, your {{ event.product_name }} is back in stock. Always include a default so an empty field does not leave a gap. Our personalization guide shows more patterns, and the Liquid reference lists the fields.

How to test subject lines properly

1. Choose one change. Test question versus statement, or specific versus general, not several differences at once.
2. Pick the right metric. Opens are inflated by mail privacy features, so judge winners by clicks or conversions where you can.
3. Split randomly. Send both versions at the same time to similar groups.
4. Use enough people. A few hundred recipients rarely settle anything. Our A/B testing guide includes a sample size calculator.
5. Record what you learn. Keep a log of tests, results and the lesson, so patterns emerge.

In Flowfox campaigns you can create up to several variants of a subject line and let the platform send the better one to the rest of the list. FoxAI can draft alternatives, which you should then edit to match your voice.

Open rates, privacy features and the law

Since mail apps began preloading images, the open rate has become a noisy number. Email tracking relies on a hidden image, and when a mail app fetches it automatically, an open is recorded even if nobody read the message. Treat opens as a rough signal for comparing subject lines inside one campaign, and rely on clicks, replies and conversions for decisions. Subject lines are also covered by law in many places. The US CAN-SPAM Act requires that a subject line must not mislead about the content, and similar rules apply elsewhere. Beyond legality, plain honesty is better marketing, because the complaint button is one tap away. If you want a wider background on the problem itself, read about email spam and how filters evolved.

Common mistakes

• Ignoring the sender name. A recognisable name often matters more than the subject.
• Optimising opens at the expense of trust. Clickbait raises opens once and unsubscribes forever.
• Copying competitors. What works for them may not suit your audience.
• Not reading it on a phone. Check how it truncates.
• Forgetting transactional emails. Receipts and reminders deserve clear subject lines too.

A subject line is a promise. The email is how you keep it.

Continue with email marketing basics, drip campaigns and the Flowfox blog.