Email client
An email client is the software application or web interface that a user interacts with to send, receive, and read emails, such as Microsoft Outlook, Gmail, Apple Mail, Yahoo Mail, or the native email app on a smartphone. Email clients are distinct from email servers: the server handles the storage and routing of email messages, while the client is the interface through which a user accesses and manages their mailbox. Email clients communicate with mail servers using standard protocols such as IMAP, POP3, and SMTP. The choice of email client has a significant impact on how email messages are rendered, since each client interprets HTML and CSS differently.
Email client diversity is one of the defining technical challenges of email marketing. Unlike web browsers, which have converged considerably on web standards over the years, email clients vary dramatically in their support for HTML and CSS features. Microsoft Outlook in particular uses Microsoft Word’s rendering engine for HTML emails, which produces significant layout differences compared to web-based clients like Gmail. Apple Mail and mobile email apps generally have strong modern rendering support. Testing emails across multiple clients is essential for ensuring consistent rendering.
For B2B email marketers, understanding which email clients your audience uses informs design and coding decisions. If your recipient base is primarily in large corporate environments, Outlook is likely their client of choice, which means designing for its limitations rather than assuming modern browser-level HTML support. Tools like Litmus and Email on Acid allow you to preview your emails across dozens of email client and device combinations before sending, catching rendering problems before they reach recipients.
Why do emails look different in different email clients?
Email clients use different rendering engines to interpret and display HTML and CSS. Web-based clients like Gmail and Yahoo Mail are relatively standards-compliant and support most modern CSS. Microsoft Outlook uses a version of Microsoft Word’s rendering engine for HTML, which has significant limitations: it does not support many CSS properties, handles fonts and spacing differently, and requires legacy coding techniques. Apple Mail and most mobile email apps have good modern support. These differences mean an email that looks perfect in one client can have layout breaks in another.
What is the most popular email client for B2B recipients?
In B2B environments, particularly in larger organisations, Microsoft Outlook is consistently the most used email client, often across both desktop and mobile through the Outlook app. Gmail is widely used in smaller companies, technology businesses, and education sectors. Apple Mail is significant among users of Apple devices. The specific breakdown for your audience can be found in the email client data reported by your email platform, which logs which clients were used to open your campaigns.
How do I make my emails render correctly in Outlook?
Outlook requires using table-based layouts rather than modern CSS flexbox or grid, and many CSS properties are not supported or behave unexpectedly. Specific practices include using inline styles rather than embedded stylesheets, coding layouts with HTML tables, avoiding background images in table cells, using HTML font attributes for font declarations as a fallback, and using conditional comments (HTML comments that Outlook specifically reads) to apply Outlook-specific styling overrides. Using an email-specific framework or template designed for cross-client compatibility is the most practical starting point.