Email subject lines: how to write ones that get opened

What people see in the inbox

In most inboxes, three things appear together: the sender name, the subject line and a line of preview text taken from the start of your email or from a preheader you set. People read them as one unit, often in under a second, and usually on a phone.

How much of the subject shows depends on the email app, the screen and the person’s font size. A phone in portrait mode shows far fewer characters than a desktop inbox. That is why the most important words should come first: if the end gets cut off, the meaning should survive.

Gmail also sorts most marketing email into the Promotions tab. That is still the inbox. People who look for your emails will find them there, so write for the reader rather than trying to trick a filter.

Before anyone reads your subject, they check who it is from. A familiar sender name is one of the strongest reasons people open. Use the name your customers know you by, such as your shop or brand name, and keep it the same from email to email.

Some brands use a person’s name with the brand, for example “Ananya from Kaapi House”. It can feel more personal for newsletters and founder notes. If you try it, keep it consistent, because a changing sender name looks suspicious.

Approaches that work

There is no single best formula. These approaches work in different situations; pick the one that fits the email you are sending.

Length, emojis, capitals and punctuation

• Put the key words first. “Diwali sale: 30% off kurtas” survives truncation; “We have some exciting news to share about our Diwali sale” doesn’t.
• Short is usually safer on mobile, but clarity matters more than a character count. A clear 50-character subject beats a vague 25-character one.
• Use emojis sparingly and only where they fit your brand. One relevant emoji can draw the eye in a crowded inbox; several look like spam. Check how it renders, since some apps show emojis differently or not at all.
• Avoid ALL CAPITALS and strings of exclamation marks or question marks. They read as shouting and are classic spam signals.
• Use the ₹ symbol for prices rather than “Rs.” if your audience is in India. It is shorter and clearer.
• Sentence case usually looks more natural than Title Case In Every Word.

Write the preview text on purpose

If you don’t set preview text, the inbox shows whatever comes first in your email, which is often “View in browser” or an image’s alt text. That wastes the second most valuable line you have.

Treat the preview as the second half of the subject. It should add information rather than repeat it. If the subject says “Your Diwali gift guide is here”, the preview might say “Ideas from ₹299, with delivery before Dhanteras”. For a cart reminder, the preview could show the cart total; for an event, the date and venue.

Personalise naturally

A first name in the subject can help, but it has become common enough that it no longer stands out on its own. Personalisation works best when it reflects something real: the city someone lives in, the product they looked at, the course they enquired about or the event they attended last year.

Always set a fallback. If a contact has no first name saved, “Hi ,” or “, your offer is here” looks careless. In MailNesto you write a merge tag with its fallback, such as {{first_name|there}}, so people without a name see “there” instead of a gap.

For large sends, spintax can vary the wording slightly between recipients, for example {{spin:Hi|Hello|Hey}}. Each person sees one version, chosen consistently for them.

Habits that cost you opens and trust

• Fake “Re:” or “Fwd:” prefixes that pretend the email is part of a conversation.
• Subject lines that promise something the email doesn’t deliver, such as “Your order update” on a sales email. They lead to complaints, and US law (CAN-SPAM) specifically prohibits misleading subject lines.
• False urgency: “Last chance” every week, or countdowns that reset. Readers learn to ignore you.
• Heavy use of “FREE”, “100%”, “Guaranteed” or “Act now”. A single “free” is fine when something genuinely is free; piling up such words raises spam filter scores.
• Changing style completely every send, so readers can’t recognise your emails at a glance.
• Writing the subject line last, in a hurry, after hours spent on the design.

Writing for Indian inboxes

Your audience may read in English, Hindi, Tamil, Marathi, Bengali or a comfortable mix. If your customers speak to you in a mix of Hindi and English on social media, a subject line in the same tone may feel natural. If you serve a professional audience, plain English is usually safer. Whatever you choose, send a test to yourself first and check that any Indian-language script displays properly on common phones and email apps.

Festivals and local references work well when they are genuine. A Pune bakery mentioning Ganeshotsav or a Kochi restaurant mentioning Onam sadhya sounds local and specific. A national brand naming every festival in every email sounds generic.

Think about when the email will be read. A subject about lunch specials makes sense at 11 am, not 9 pm. Sending in each subscriber’s time zone, or at the hour they usually open, helps the subject land at the right moment.

Subject lines by email type

Test, don’t guess

1. Test one thing Compare two subject lines that differ in one idea, such as a question versus a statement, or with and without the price. Testing two unrelated subjects tells you little you can reuse.
2. Use a test group Send each version to a random share of the list, for example 10% each, and send the winner to the rest once the test ends.
3. Pick the right measure Apple Mail Privacy Protection and security scanners can register opens that never happened. Where you have enough volume, judge by clicks, or at least confirm the open winner also won on clicks.
4. Give it enough time Wait a few hours before choosing a winner, so people who check email later in the day are counted.
5. Write down what you learned Keep a simple log of each test and its result. After a few months, patterns for your own audience will matter more than any general advice.

In MailNesto you can A/B test the subject line (with its own preview text), the sender name, the content or the send time. Choose the test group size, whether opens or clicks decide the winner and how long to wait, from 1 to 72 hours, and the winner goes to the rest of the list automatically. Machine opens and scanner clicks are filtered out of reports.

Tools that help

The AI assistant in MailNesto suggests several subject lines with matching preview text in your tone, which is useful when you are stuck. Treat the suggestions as drafts and edit them to sound like you.

The free subject line tester on our website scores a subject, shows how it looks on a phone and a desktop inbox, and counts characters, words and emojis. The pre-send spam check flags risky wording in the full email.

If an important campaign had a weak subject line, resend it to people who didn’t open with a new subject. Use this sparingly, for emails that really matter, since repeated sends to the same people can raise complaints.