Email Client
Software or apps people use to read, send, and manage email, such as Gmail or Apple Mail. Different email clients can display the same email in different ways, which affects how your emails look and perform.
Also known as Email Program, Email App, Client
An email client is the app or program someone uses to read and send email. It might be Gmail in a browser, Apple Mail on a Mac, or the Mail app on a phone. When people talk about the inbox, they are talking about what they see inside that client.
Email clients matter because each one reads your HTML in a slightly different way. Fonts, spacing, buttons, and images can all shift from one client to another. If you design only for one client, a big part of your list may see a broken or messy layout. That hurts trust and can lower clicks and sales.
A simple way to work with email clients is to use clean layouts and test early. Send test emails to a few main clients that match your audience, like Gmail, Apple Mail, and Outlook. Check how the email looks on both desktop and mobile. Fix the worst issues first so everyone at least gets a clear and readable message.