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Tools & Platforms

Email Client

Software or app used to read, compose, and manage email messages.

Definition

An email client is a software application or web service that allows users to send, receive, and manage their email. Email clients can be desktop applications (Outlook, Apple Mail, Thunderbird), web-based services (Gmail, Yahoo Mail, Outlook.com), or mobile apps. Each client renders HTML emails differently, which affects how your emails display.

Why It Matters

Email clients vary significantly in how they display HTML emails. What looks perfect in Gmail might break in Outlook. Understanding the email client landscape helps you design emails that work everywhere and prioritize testing for your audience's most-used clients.

How It Works

Email clients connect to mail servers using protocols like IMAP or POP3 to retrieve messages and SMTP to send them. They render HTML and CSS to display formatted emails, but each client has its own rendering engine with different capabilities and quirks. Some clients block images by default or strip certain CSS properties.

Best Practices

  • 1Test emails in the clients your audience uses most
  • 2Use email-safe HTML and CSS (table-based layouts, inline styles)
  • 3Always include a plain-text version as fallback
  • 4Consider how images display when blocked
  • 5Monitor email client share in your analytics

Frequently Asked Questions

As of 2024, Apple Mail and Gmail dominate, together accounting for 60-70% of opens. Outlook remains important for B2B audiences. Check your own analytics for your audience's specific client distribution.

Outlook uses Microsoft Word's rendering engine, which has limited HTML/CSS support. It ignores many modern CSS properties, requires table-based layouts, and has VML fallbacks for some features. Test specifically for Outlook.

Yes, as dark mode adoption grows. Test how your emails appear in dark mode (many clients auto-invert colors). Use transparent PNGs for logos, avoid all-white backgrounds, and consider adding dark mode specific CSS where supported.