Preview & test
MailInApp builds each email in several versions, and the studio lets you check every one before you send: on a phone, after someone has answered, and as a particular email app shows it.
Desktop and phone
The Device switch above the canvas shows the email at desktop width or on a 375 px phone, with its phone settings applied. In Preview, Side by side shows both at once. The mailed tiers render the phone view in a real 375 px frame, so the email's own phone rules apply exactly as they will in an inbox.
Preview tiers
In Preview, the tier switch picks what you see:
- Live view: the hosted web version recipients open from a link.
- Mailed: the HTML that's mailed, as a modern email app reads it.
- Outlook: the mailed HTML with classic Outlook's own branches forced, so you see its version without owning a copy.
- Clients: the mailed HTML as one email app shows it (see below).
The dark-mode toggle next to them shows the email in dark mode, the way the chosen tier or app would draw it.
Preview states
Interactive blocks show a Preview state menu on the canvas. Pick a state to see the block as a recipient would after acting on it. The states are Answered (with the answer you pick), Submitted, Booked, Closed, Revealed, Won (with the prize you pick), a form's Wizard page, Sold out, Saved for later, Ended and Before it opens. A badge on the block says which state you're previewing.
For blocks that show results, Simulated results lets you type numbers (votes per option, ratings and an average, an NPS, thumbs up, people going) and see the results bar or image with them.
States and simulated numbers are a preview only: they're never saved with the email or sent.
Each email app
The Clients tier shows the email as a chosen Email app shows it: Mail on iOS, iCloud Mail, Thunderbird, each Gmail app, Outlook.com and the Outlook apps, and Yahoo Mail. It's a simulation built from real-inbox measurements, not a screenshot, and under the email it lists which blocks run there, which show their fallback, what forms do in that app and what it does in dark mode. Each app has its own phone width and dark mode controls.
Real screenshots. On the Pro plan and up, connect Mailgun Inspect in Settings › Integrations and press Take real screenshots to see the email in real inboxes, next to the simulation. Screenshots use the previews included in your Mailgun plan.
Where each block works
Every interactive block shows a Where it works line in the Inspector, and the same line as a tooltip in the Insert panel: which apps run it in the email, which show its fallback, and which aren't measured yet. A one-tap block (poll, rating, RSVP, booking) says it works in every app, since each choice is a link confirmed on a web page. The lines come from the same measurements as Email client support.
To write words for only one version, such as "Tap to vote on the web" under a poll in apps that fall back, use a block's Show in setting.
Preflight check
🔍 Pre-Flight Check reviews the email before it goes out, sorted into tabs:
- Accessibility: color contrast in light and dark mode, heading order, alt text (required on a linked image), link text like "click here", the email's language, and tap targets that are too small.
- Links: every link is checked live, with its status code and redirects; links that aren't https and tracked links without UTM tags are flagged.
- Deliverability: the Gmail clip size, too many images for the text, spammy phrases, all-caps, link shorteners, and link text that names a different site than the link goes to.
- Email apps: blocks without a working fallback, corners or backgrounds classic Outlook won't draw, and web fonts that fall back.
- Content: empty or incomplete blocks, such as a tab with no title or a coupon with no code.
Many issues have a Fix button that applies the fix for you (adding alt text, swapping a color for one with enough contrast). The Gmail clip meter under the canvas shows the email's size as you work: Gmail clips an email past 102 KB, hiding the rest, unsubscribe link included.
Subject, preheader and test sends
The studio's header holds the email's Subject and Preheader, the preview line inboxes show after the subject. They're the same fields as on the send page.
Send test mails the email to up to 5 addresses. Preview as picks a recipient row, so merge tags and display conditions resolve as they will for that person. On a gallery template's page, Send me this example mails the template to your own address.