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Mail clients don’t all render HTML the same way. Outlook for Windows, Gmail and Apple Mail can show the same email quite differently, and dark mode recolours it again. InstantCampaign gives you two ways to check before you send:
  • Inbox previews take real screenshots of your email in real mail clients through your own Litmus or Email on Acid account. Available on the Pro and Enterprise plans.
  • Dark mode preview shows a simulation of how dark-mode clients recolour your email. It’s free on every plan and needs no other account.

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Connect Litmus or Email on Acid

  1. Go to Settings → Integrations and find Inbox previews.
  2. Choose Litmus or Email on Acid.
  3. Enter your API key. For Email on Acid, also enter your account password: Email on Acid signs API requests with both.
  4. Optionally, list the clients to capture (see below), then click Connect.
  5. Click Test connection to check the vendor accepts your credentials.
You need permission to manage integrations. Your key is stored encrypted and is never shown again. To change other settings without retyping it, leave the key field blank and click Save. Disconnect deletes the stored key. Past previews and their screenshots stay.

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Choosing clients

  • Litmus: enter Litmus client codes separated by commas, such as OL2019, IPHONE16, CHROMEGMAILNEW. If you leave the field blank, ten common clients are captured: Outlook 2019, Outlook for Windows, Apple Mail, iPhone 16 (light and dark), Gmail on iPhone and Android, and Gmail, Outlook.com and Yahoo Mail on the web. Litmus bills each capture, so a shorter list costs less.
  • Email on Acid: enter Email on Acid client IDs such as outlook16, iphone6p_9. If you leave the field blank, your Email on Acid account’s default clients are used.

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Run an inbox preview

  1. Save your template. The preview uses the saved version.
  2. In the builder, open the Deliverability score panel from the toolbar and click the Inbox preview tab.
  3. Click Run preview.
Screenshots appear as each client finishes, usually within a minute or two, grouped into Desktop, Mobile and Webmail. Click a thumbnail to see the full screenshot. A client that couldn’t render the email is marked so, and the rest still show. The email is rendered the way a test send renders it: in the template’s default language, with your sample data, a stand-in recipient, and the footer. If the template belongs to a campaign email, that email’s subject line and preheader are used. On the campaign plan page, each email shows a short Last inbox preview line once it has one.

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Allowance and repeats

If you run a preview again and nothing has changed in the email, the earlier result is shown and nothing more is used. A preview that the vendor refuses doesn’t count. Each run is also a test on your own Litmus or Email on Acid account, so their pricing applies. Screenshots are copied to InstantCampaign’s storage as soon as they’re ready, so they keep working after the vendor’s own links expire.

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Dark mode preview

In the builder’s Preview tab, use the moon switch above the email: Images are never recoloured. That’s what makes a dark logo on a transparent background disappear in dark mode, so check logos and any text that’s part of an image. If your email has no dark-mode CSS, a note above the preview says so. That’s not an error: the inverting clients recolour the email on their own. The dark mode preview is a simulation. Each client has its own rules, so use an inbox preview of the clients’ dark variants (such as iPhone 16 Dark) when it matters. The dark mode preview also works when you preview as a contact.