HTML preview & responsive testing

The HTML preview

When you open a captured message, the HTML tab renders its markup in an isolated frame — a browser rendering of the HTML your app sent, not a simulation of any specific email client. Preview responsive layouts here, then pair it with the HTML & CSS compatibility check below to flag email-client compatibility issues before an email ever goes out for real.

The HTML preview renders the message's markup in an isolated frame.

Alongside the preview you can inspect the source, headers and raw message, run the HTML & CSS compatibility check, and check the spam score.

Responsive widths

Emails are read everywhere, so the preview lets you switch the viewport width to check your responsive design:

• Fit — scales the message to fit the available space
• Tablet — renders at a tablet-sized width
• Mobile — renders at a narrow phone width, where most email is opened

Switching widths triggers your media queries, so you can catch layouts that break on small screens before your client does.

Test mobile first

A majority of email is opened on phones. Check the mobile width on every template before sharing it for approval.