Definition
Email client preview is the visual appearance of an email when viewed in a specific email client or on a specific device. Because email clients use different rendering engines, the same email can look significantly different in Gmail, Apple Mail, Outlook, and other clients.
Understanding email client preview differences is essential for professional email marketing. An email that looks perfect in your test environment may break in a clients used by a significant portion of your subscribers.
Major Email Client Rendering Engines
| Client | Rendering Engine | CSS Support Level |
|---|---|---|
| Apple Mail | WebKit | Excellent |
| Gmail (web) | Custom (strips many CSS) | Limited |
| Gmail (mobile app) | WebKit | Good |
| Outlook (Windows) | Microsoft Word | Poor |
| Outlook (Mac) | WebKit | Good |
| Outlook (mobile) | WebKit | Good |
| Samsung Mail | WebKit | Good |
| Yahoo Mail | WebKit | Moderate |
Common Rendering Differences
| Element | Gmail | Apple Mail | Outlook (Windows) |
|---|---|---|---|
| CSS media queries | Supported | Supported | Not supported |
| Background images | Limited | Supported | Not supported |
| Custom fonts | Not supported | Supported | Not supported |
| CSS padding | Supported | Supported | Inconsistent |
| Bulletproof buttons | VML not supported | VML not supported | VML supported |
How to Test Email Client Preview
- Use testing tools: Litmus and Email on Acid provide previews across 100+ email clients.
- Test top 10 clients: Cover the 10 most used clients by your audience. This typically covers 90%+ of your opens.
- Test on real devices: Preview tools are good, but testing on actual phones and computers catches issues that simulators miss.
- Test both loading and image-blocked states: Many clients block images by default. Test how your email looks with and without images.
- Establish a QA checklist: Create a standardised checklist for email testing that covers critical rendering elements.
Common Preview Issues
- Broken layout in Outlook: Outlooks Word-based rendering breaks modern email CSS.
- Gmail CSS stripping: Gmail removes or ignores certain CSS properties.
- Mobile font too small: Text that looks fine on desktop is unreadable on mobile.
- Image overflow: Images wider than the email container break layouts on narrow screens.
- CTA button not rendering: Button codes that work in most clients break in specific clients.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
AIDA Model for Email
The AIDA model (Attention, Interest, Desire, Action) is a classic copywriting framework used to structure email campaigns that guide subscribers from awareness to conversion.
AMP for Email
AMP for Email is a Google-developed framework that allows email messages to include interactive elements like forms, carousels, accordions, and live content. It turns static emails into dynamic, interactive experiences directly inside the inbox.
Anchoring Effect in Email Marketing
The anchoring effect is a cognitive bias where the first piece of information presented (the anchor) influences subsequent decisions, used in email to frame pricing and value perception.
Announcement Email
An announcement email is a dedicated campaign that communicates a specific update, milestone, or change to subscribers, from product launches and feature releases to company news and events.
Frequently Asked Questions
Test the top 10 clients used by your audience. Most ESPs provide client usage data. If you do not have this data, a standard test set includes Gmail (web + app), Apple Mail (iOS + macOS), Outlook (2019, Microsoft 365, mobile), and Samsung Mail.
Outlook for Windows is consistently the most challenging client because it uses Microsoft Words rendering engine, which does not support modern email CSS. Conditional code (VML and `2026 Email Calculator. All rights reserved.