Definition
The email subject preview — commonly called the preheader or preview text — is the line of text a recipient sees next to or under the subject in the inbox. It extends the subject's message and is one of the few elements that decides whether someone opens an email.
Because most clients now show a preview, treating it as a second subject line maximises the chance of a click to open. A well-written preview complements the subject, adds value, and gives the recipient another reason to open.
Where the Preview Shows
| Email Client | Preview Behaviour |
|---|---|
| Mobile inbox | Short snippet, often truncated |
| Gmail | Preview text under the subject |
| Outlook | Shows preview in some layouts |
| Heavy truncation | Only the first characters survive |
Clients vary, so the first words matter most.
Why the Preview Matters
- Extends the subject: Adds detail the subject cannot hold.
- Raises open rate: A compelling preview supports the open decision.
- Uses the first words well: Truncation means the opening matters most.
- Complements the design: Restores default snippet text that adds nothing.
How to Optimise the Preview
- Write a genuine preview: Avoid leaving the first body text as the snippet.
- Complement the subject: Add information rather than repeat it.
- Front-load the value: Put key words first for truncation.
- Match the promise: Keep the preview consistent with the email content.
Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Management
Bounce management is the process of handling emails that are rejected by mailbox providers, including classification, removal of bad addresses and protection of sender reputation.
Frequently Asked Questions
A subject preview, or preheader, is the short snippet shown in the inbox beside or under the subject line. It extends the subject and helps the recipient decide whether to open the email.
Most email clients display a preview, so it works as a second subject line. A good preview raises the chance of an open, while a default snippet of body text wastes valuable inbox space.
Keep the most important words at the start, since most clients truncate after a certain number of characters. A concise preview that delivers its value early is the most reliable approach.
Not by repeating it. The preview should complement the subject, adding extra detail or value that makes the recipient more likely to open, while staying consistent with the email's actual content.