Preheader

A preheader is the short line of text an inbox shows beside or beneath the subject line. It is the third and last thing visible before somebody decides whether to open a message, and on most sends it was never written by anybody.

In short

• It is the preview text an inbox shows next to the subject line.
• Left unset, it fills with whatever the message starts with.
• Repeating the subject line wastes the only spare space you have.
• It is cut short on a phone, so the useful part goes first.

Where it appears and what it competes with

An inbox row holds three fields, read in a fixed order.

• The from name. Who this is from.
• The subject line. What it is about.
• The preheader. A few more words, taken from the message or written for the slot.

The three share one line of space in most inboxes, which is the detail that explains almost everything about how a preheader behaves. A long subject line leaves less room for the preheader. A short one leaves more. The boundary between them moves depending on the device, and neither field can be planned as though it had a fixed length.

What fills it when nobody decides

Every email has a preheader whether or not anybody wrote one, because the inbox will take the first readable text it finds in the message.

That text is rarely the sentence you would have chosen. The usual candidates are a line offering to view the message in a browser, an unsubscribe notice sitting above the content, a company address, or the alt text attached to a logo. Some templates produce a preview that is nothing but the word Logo.

This is the cheapest fault in email marketing to fix and one of the most common to find, because it is invisible from inside the sending tool. The message looks correct in a preview window and looks careless in the place it is actually judged. The only reliable check is to send a test to yourself and look at the inbox list rather than at the opened message.

Writing one that earns its space

The rule that does most of the work: extend the subject line, do not repeat it.

A subject line is short and has to be understood alone. A preheader is the room to add the thing that would not fit. If the subject names a sale, the preheader carries what is in it and when it ends. If the subject asks a question, the preheader hints at the shape of the answer. Read together they should sound like one sentence and one voice.

Two habits carry the rest. Front load it, because the cut comes early on a phone and a preheader that reveals its point at the end becomes meaningless the moment it is truncated. And keep it honest, since a preview that overstates the contents raises the open rate of one campaign at the cost of every campaign after it.

The hidden preheader and why it costs something

A widely shared technique is to write a preheader into the message and hide it, so the inbox reads the text but the opened email never displays it.

It works on most clients and it has two prices. The first is that the message a reader was promised in the preview does not appear anywhere once they open it, which is a small disappointment repeated on every send. The second is that hidden text is a pattern filters have reason to be suspicious of, and while a single hidden line is not going to send you to a spam folder, it is a technique that argues for itself rather than for the reader.

The alternative is duller and better. Write an opening line for the message that also works as a preview, and let it be visible in both places. Any email template built properly has room for a first line that says something.

Setting one, and checking it

The field exists in every serious sending tool, and it is rarely where somebody new expects to find it. Depending on the platform it is labelled preheader, preview text or snippet, and it sits beside the subject line in the campaign settings rather than inside the message content.

Three habits cover most of the ground.

• Write it at the same moment as the subject line. They share a row in the inbox and they should be written as one thought. Writing them a day apart is how a preview ends up repeating the subject.
• Send a test and look at the list, not the message. The only place a preheader can be judged is an inbox. Open the test on a phone as well, since that is where the truncation is severe.
• Check the automated messages too. Order confirmations, delivery updates and the messages in an email flow are sent far more often than campaigns and are almost never reviewed. A default preview reading Unsubscribe goes out with every one of them.

The last of those is where most of the value sits. A campaign is written by somebody paying attention. An automated message was set up once, possibly by somebody who has left, and has been sending ever since.

Words you will hear

• Preview text. What the inbox shows. Used interchangeably with preheader.
• Snippet. Another name for the same field, common in some sending tools.
• Johnson box. An older direct mail term for a summary placed before the main body, occasionally used for the visible version of a preheader.
• Truncation. The point where an inbox cuts the line off.
• Alt text. Image descriptions, which an inbox will read into the preview slot if there is no text above them.

A preheader takes about a minute to write and is set once per campaign. It is one of the few fields in email where the difference between doing it and ignoring it is visible to every recipient before they have opened anything.