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Email Subject Line Best Practices
Ten practical rules for subject lines that get opened for the right reasons, and a preview builder to see your subject, preview text and sender name together the way the inbox shows them.
Build your inbox row
No preview text set, so the inbox fills the space with whatever comes first in the email, like “View this email in your browser”.
The rules
- Say what's inside. The clearest reason to open beats the cleverest wordplay.
- Front-load it. The first 30–35 characters must work alone on a phone. See where lines get cut.
- Be specific. Numbers, dates, names and outcomes beat adjectives.
- Write to one person. “You” and plain language outperform corporate voice.
- Keep promises. The first paragraph must deliver what the subject promised.
- Use urgency only when it's real. Fake deadlines teach readers to ignore you.
- Skip the spam habits. ALL CAPS, !!!, “act now”, “100%”. Full list.
- Set preview text. Otherwise the inbox shows “View in browser” or your logo's alt text.
- Use emoji sparingly. One relevant emoji can stand out; test it against the plain version and check it renders.
- Test two angles, not two words. A/B test a question against a benefit, not “Save” against “Get”.
Preview text: the second subject line
Preview text (preheader) is the snippet most inboxes show after the subject. On phones it's often two lines, which is more room than the subject itself. Use it to add the detail the subject didn't have space for.
Keep it roughly 40–100 characters. If your email platform has a preheader field, use it; otherwise the inbox takes the first text in the email body. Some senders add invisible spacing characters after the preheader so the inbox doesn't pull in the rest of the email.
Emoji in subject lines
Emoji render in most modern inboxes, including Gmail, Apple Mail and Outlook, though they can look different on each and very old clients may show a box. Use one, place it where it supports the meaning, and never replace a key word with it: screen readers announce emoji by their names, so a subject full of them sounds strange.
Personalisation
A first-name merge tag can help, but it's now common enough that it rarely surprises anyone. Personalisation that reflects behaviour, like the product they viewed or the city they're in, tends to be more meaningful. Always set a fallback for empty fields so nobody gets “Hi ,”.
Frequently asked questions
What are the best practices for email subject lines?
Say what is inside, keep the key words in the first 30–35 characters, be specific, write to one person, keep the promise in the email, avoid fake urgency and spammy formatting, set preview text, and A/B test different angles.
Should I use emojis in email subject lines?
Sparingly. One relevant emoji can help a line stand out, especially for consumer brands. Test against the plain version, check how it renders, and don't replace key words with emoji because screen readers read out their names.
How long should preview text be?
Roughly 40–100 characters. Phones often show two lines of preview text; desktop inboxes show whatever fits after the subject on the same line.
Should subject lines be in title case or sentence case?
Either works if you are consistent. Sentence case tends to read as more personal; title case can look like an ad. For cold emails, many senders use lowercase or sentence case.