Which webmail messaging services dominate the market?

Who controls the inbox still controls a part of the customer relationship. As digital channels multiply, the email remains one of the most effective tools in marketing. But for a message to reach its target, it must be well-rendered, well-delivered, and well-received. Rather than stopping at sending platforms, today we focus on the most popular webmail services this year. Let’s go!

1# Gmail

At the top of the global ranking without much surprise, Gmail remains, the most used email service worldwide. This webmail service continues to attract with its speed, simplicity of interface, and especially its perfect integration into the Google ecosystem: Drive, Calendar, Meet, but also Google Ads and Analytics for professionals.

On the technical side, Gmail offers a globally reliable HTML rendering, supports AMP for Email and handles images well. But it also applies strict rules regarding deliverability and security (SPF, DKIM, DMARC required). For an online marketing expert, not optimizing campaigns for Gmail means ignoring a massive part of their audience.

Also to note: Gmail automatically sorts messages into tabs (primary, promotions, etc.), which requires fine-tuning the subject line, the pre-header, and the sender’s reputation to avoid dead zones in the inbox.

2# Outlook / Microsoft 365

For a long time surpassed by Gmail, Outlook is regaining ground and experiencing a true revival in professional environments. It has become the most adopted email client in businesses, according to several market reports, mainly due to the evolution of Office 365 (Microsoft 365), which has successfully integrated collaboration (Teams), cloud (OneDrive), and productivity tools.

In terms of email rendering, Outlook remains quite fickle. It uses a rendering engine based on Microsoft Word, making it less compatible with some modern CSS elements or complex layouts. Developers thus need to plan for specific adjustments, often tedious, to ensure a smooth reading on Outlook desktop. That said, its market share in B2B largely justifies the investment: ignoring Outlook is risking poorly addressing professional leads.

3# iCloud Mail (Apple Mail)

The Apple universe maintains a colossal influence on email consultations. According to Litmus data from February 2025, Apple Mail, all versions combined (iPhone, Mac, iPad), accounted for 50.2% of email openings. The success of this email client is based both on its quality of rendering and its accessibility as it is installed by default on all Apple devices.

But since the introduction of Mail Privacy Protection (MPP), Apple Mail has disrupted the traditional indicators of email marketing. By masking openings and IP addresses, it renders open rates unreliable, forcing professionals to revise their performance metrics. Campaigns must therefore be designed more around post-click behavior than mere openings, particularly on the increasingly numerous Apple segments.

4# ProtonMail

In a context heavily marked by data protection, ProtonMail is gaining popularity, especially among users concerned about their privacy. This year, the Swiss end-to-end encrypted service becomes notably the go-to mailbox for certain sensitive sectors such as finance, healthcare, and legal, and for part of the European audience.

ProtonMail operates without advertising, tracking, or data recovery. However, it also has its constraints: its encryption mode complicates the reception of complex HTML marketing messages, and its SMTP/IMAP incompatibility in its free version makes API or CRM connections difficult. It is therefore a channel to consider for “privacy-respectful” campaigns, but requires suitable technical settings and perhaps a specific editorial approach (clear texts, without graphic dependency).

Alternative Free Services

Although often relegated to second place, free services like Yahoo! Mail, GMX, or Mail.com retain a loyal user base. Yahoo!, for instance, continues to be widely used in the United States and Japan, while GMX is popular in Germany.

They sometimes feature more heterogeneous infrastructures, with spam filters less sophisticated than Gmail or Outlook, but also volume, quota, or display constraints.

For global campaigns, it remains essential to test the appearance and deliverability of emails on these services, at the risk of missing out on a specific audience, often scarcely targeted by competing actors.

The table above provides an overview of the most used webmails (sources: Wikipedia/Mailchimp) and the email domains most frequently verified by CaptainVerify. Unsurprisingly, Gmail overwhelmingly leads the ranking, followed by historic services like Outlook or Yahoo Mail. These platforms continue to attract a large user base thanks to their accessibility and their integration with other digital services.

Domains like wanadoo.fr, neuf.fr, or laposte.net are still very present, although they are no longer actively promoted by their providers. Their persistence shows users’ attachment to their old addresses, often linked to old internet subscriptions or ingrained personal uses.

Some Concrete Recommendations for E-Marketers

To make the most out of your email strategy, start by systematically testing your campaigns on the three clients that dominate openings: Gmail, Outlook, and Apple Mail. Each of these platforms presents different technical requirements, which necessitates adapting design and content to ensure a consistent experience.

Closely monitor deliverability: correctly configuring your SPF, DKIM, and DMARC records is no longer optional. Without these settings, your messages risk being rejected or sent directly to spam. For segmented campaigns, also consider adjusting sending times based on the client type: Apple users often check their mail on mobile upon waking, while Outlook users do so mainly on desktop during office hours.

Finally, anticipate behavior changes. Focus your analyses on reliable KPIs such as clicks, conversions, and unsubscribe rates. This will allow you to better manage your campaigns while respecting your recipients’ privacy.

In summary, email is a complex ecosystem where each email client has its own rules and filters. Mastering the specifics of the most used services means mastering the variables that determine whether your message will be seen, ignored, or deleted.