Writing Subject Lines and Preheaders for Transactional Email

Marketing subject lines are written to entice — to earn a click in a crowded inbox. Transactional subject lines have almost the opposite job: the recipient already wants this email, so your only task is to make it instantly, unmistakably recognizable. Clever gets in the way. Clear wins.

The subject line: say exactly what it is#

The best transactional subject line describes the email so plainly that the recipient knows what it is before opening — and can find it later by searching.

"Reset your password." "Your receipt from Acme, order #10432." "Confirm your email address." "Your export is ready to download."

Notice what these have in common: they're specific, they front-load the important words, and they include useful details (an order number, an action) that make the message findable and trustworthy. There's no curiosity gap, no emoji, no marketing voice — because anything that smells like marketing on a transactional message both confuses the recipient and nudges spam filters in the wrong direction.

Front-load the key words, too. Many people read subject lines on a phone where the line gets truncated, and inbox previews cut off early. "Your password reset link" reads better at a glance than "Here is the link you requested to reset the password for your account."

The preheader: the second line you forget to write#

The preheader is the snippet of text mail clients show right after the subject line, pulled from the top of the email body. If you don't set it deliberately, clients grab whatever comes first — often something useless like "View this email in your browser" or a stray alt-text.

Treat the preheader as a second subject line. Use it to add the detail the subject couldn't fit: "Valid for 30 minutes. If you didn't request this, ignore this email." For a receipt: "Order #10432 · $48.00 · shipping to Madrid." It's free real estate that makes your message more useful and more obviously legitimate at a glance.

A few rules of thumb#

Keep the subject short enough to survive truncation. Include an identifier — an order number, an account name — where it helps the recipient place the message. Match the tone to the transaction: a security email should read as serious, not chirpy. And keep it consistent, so a returning user recognizes your receipts and confirmations instantly from the subject line alone.

The whole philosophy of transactional copy is service, not persuasion. The recipient is already on your side. Your job is just to be clear, and to get out of their way.