Email Preview Text: The Hidden Conversion Booster
The second line nobody writes, what happens when you leave it empty, and how many characters each client shows.
On this page
The short version
- Leaving preview text empty does not produce a blank space. The client pulls the first text it finds, which is usually a view-in-browser link or an alt attribute.
- It should extend the subject line, not repeat it. Repetition wastes the second most valuable line in the whole message.
- Roughly forty characters survive on a phone — the same constraint as the subject, applied to a line most senders never write at all.
Preview text is the line of grey text that follows the subject in an inbox list. It is the second thing a reader sees, it is under your control, and in a large share of commercial email it is left to whatever the client happens to find first.
What it finds is rarely good. A message that opens with a view-in-browser link previews as 'View this email in your browser', and one that opens with a logo image previews as the alt attribute — often the company name repeated, or nothing at all.
Preheader, preview text, Johnson box
Three names for roughly the same thing, which is part of why it gets skipped. Preview text is what the inbox list displays; the preheader is the block of markup at the top of the email it is usually pulled from. Some platforms expose a dedicated field and hide the mechanism entirely.
What shows when you leave it empty
| What the email starts with | What the inbox displays |
|---|---|
| A view-in-browser link | "View this email in your browser" |
| A logo image with alt text | The company name, repeated after the from name |
| A logo image with no alt text | Nothing, or the file name |
| A tracking pixel then a heading | The heading, repeating the subject line |
The first row is the most common commercial email preview line in existence, and it tells the reader precisely nothing about the message.
Write it as the second half of a sentence
The subject and the preview are read together, in sequence, as one unit. The most reliable way to write the preview is to treat the subject as the claim and the preview as the qualifier — the part that says who it applies to, what it costs, or how long it takes.
That framing also stops the most common mistake, which is writing a preview that restates the subject. Two lines saying the same thing occupy the space of two lines and do the work of one.
The pair working and not working
Preview repeats the subject
- Subject: Nine things that trip spam filters
- Preview: Learn what trips spam filters
- Subject: Your SPF record is probably over the limit
- Preview: SPF records and the ten lookup limit
Preview extends the subject
- Subject: Nine things that trip spam filters
- Preview: Six are about behaviour, not words
- Subject: Your SPF record is probably over the limit
- Preview: Two minutes to check, one DNS edit to fix
Length and the padding trick
The visible budget is similar to the subject line — roughly forty characters on a phone, more on desktop. Write to the short end.
There is a common technique of padding the preheader with invisible characters so the client stops pulling body copy in after your line runs out. It works, and it has a cost: some clients render the padding as a run of blank space, and overzealous padding is one of the patterns filters have learned to notice. If you use it, keep it short.
What to put there when nothing obvious fits
Not every email has a natural qualifier. When one does not present itself, three fallbacks are better than leaving it empty: the time cost ('a four minute read'), the specific benefit ('the checklist is at the bottom'), or the scope ('for anyone still on the old plan').
All three are honest, all three help the reader decide, and all three are better than the browser link.
Preview text check
- A preview line is set on every send, including automated ones
- It extends the subject rather than repeating it
- The point survives the first forty characters
- The preheader is hidden in the body and visible in the list
- Automated flows have been checked too — they are the ones that get skipped
Frequently asked questions
Does preview text affect deliverability?
Not directly. It affects open rate, and open rate is one of the engagement signals that feeds placement over time, so the connection is real but indirect. Heavy-handed padding is the one part that filters look at on its own.
My platform has a preview text field. Is that enough?
Usually yes — it writes the hidden preheader for you. Send a test and check the inbox list rather than assuming, because a template with its own hard-coded preheader will override the field silently.
Should transactional emails have preview text?
Yes, and they benefit disproportionately because they are opened at a high rate. Putting the order number or the delivery date in the preview means a proportion of recipients get their answer without opening at all, which is a service rather than a lost open.