Email Client Share

Email Client Share: What It Is & Why It Matters

Email client share is the breakdown of which email applications — Gmail, Apple Mail, Outlook, Yahoo Mail, and others — your subscribers are using to open and read your emails, expressed as a percentage of total opens. It’s an audience composition metric, not a campaign performance metric. Rather than telling you how an email performed, it tells you where it landed.

The mail client usage report provides a complete breakdown of the different email clients used to view an email — breaking down clients by different versions, providing a percentage of each client share across the whole campaign, and an average percentage against all available data for comparison.

Every email client renders HTML and CSS differently. A layout that looks perfect in Gmail might break in Outlook. A design that’s flawless on Apple Mail might display oddly in a browser-based Yahoo inbox. Knowing which clients your audience actually uses turns that problem from guesswork into a concrete priority list.

The Most Common Email Clients

Global email client share is dominated by two platforms, with everything else a distant third. Apple leads email client market share at approximately 57%, followed by Gmail at 30%, Outlook at 4%, and Yahoo at 3%.

That 57% Apple figure comes with an important asterisk. Since Apple introduced Mail Privacy Protection (MPP) with iOS 15 in 2021, Apple devices automatically pre-load tracking pixels — which inflates Apple’s measured share and makes open rate data less reliable.

Apple MPP permanently altered the landscape of email client tracking — email marketers can no longer rely on open rate data as an effective measure of email marketing performance or engagement.

Gmail and Apple together account for roughly 85–90% of global opens, which shapes most email design and testing decisions by default.

Why Email Client Share Varies by Audience

Here’s where global averages get unreliable fast. The market-wide split between Apple and Gmail doesn’t automatically reflect your list. A B2B SaaS company sending to IT managers will see a very different mix than a DTC consumer brand sending to millennial shoppers. Enterprise environments skew heavily toward Outlook. Consumer ecommerce lists often skew Apple.

Geographic location matters too — Germany has a significant share of GMX and Web.de users, barely visible in global data.

Only relying on global averages when deciding where to focus your testing efforts has two risks: you might put your troubleshooting resources into email clients that aren’t relevant to your audience, or you might ignore a rendering issue because a client isn’t globally popular without realizing it’s heavily used by a large part of your audience.

Your specific audience’s client share — not the industry benchmark — is what should actually drive your design and testing decisions.

How Email Client Share Is Measured

Most email platforms and analytics tools track client share using the same invisible tracking pixel that measures opens. When an email is opened, the pixel fires and passes back information about the environment — including the client, device, and operating system.

If you send email marketing campaigns, your subscribers open those messages in email clients. Each client renders HTML and CSS differently, so an email that looks perfect in Gmail might break in Outlook. Understanding which clients your audience uses — data you can pull from your email reporting — helps you prioritise which rendering quirks to fix first.

Tools like Litmus provide particularly detailed breakdowns, including which specific versions of clients are in use — useful because Outlook 2016 and Outlook 2019 can render the same email very differently.

Why Email Client Share Matters

Knowing your client share distribution shapes every technical decision you make about an email. It tells you which rendering environments to test in, which HTML workarounds to build, and where to invest your optimisation time.

There are about 1,000 different email clients out there — and they all use different rendering engines to display your email. Not only that, but certain features aren’t supported across all email clients, like animated GIFs, background images, or embedded video.

A dark mode-related visual glitch in Apple Mail is worth fixing if 60% of your list is on Apple devices. The same issue in a client representing 0.3% of your opens probably isn’t worth the engineering time.

Client share data also informs how you interpret engagement metrics. If Apple MPP opens account for a large chunk of your measured opens, your open rate is inflated — and knowing that helps you lean more heavily on click rate, CTOR, and revenue per email as your primary performance signals.

Key Takeaways

• Email client share is the percentage breakdown of which email applications — Apple Mail, Gmail, Outlook, Yahoo, and others — your subscribers use to open your emails.
• Globally, Apple leads with around 57% of email client market share, followed by Gmail at 30%, with Outlook and Yahoo each under 5%.
• Global averages rarely match your specific audience — client share varies significantly by industry, geography, and demographic, making your own list data the more useful benchmark.
• Apple’s Mail Privacy Protection has significantly distorted open-based tracking since 2021, inflating Apple client share figures and making open rate an unreliable standalone metric.
• Email client share directly informs design and QA decisions — knowing which clients your subscribers actually use means you can focus rendering tests and troubleshooting where they’ll actually make a difference.