What is an email client?
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An email client is the software you use to read and send email. Think Outlook, Apple Mail, Gmail (when you use the app), or Thunderbird. It's the interface. The thing you click "Send" in.
What it actually does: connects to your mail server to fetch messages (using IMAP or POP3) and sends outgoing mail (using SMTP). The client is what you see. The server is the engine doing the heavy lifting behind the scenes.
Two flavors: desktop clients (Outlook, Apple Mail, Thunderbird) live on your computer and sync with the server. Webmail (Gmail in a browser, Outlook on the web, Yahoo Mail) runs in your browser and doesn't install anything. Both are email clients. The difference is where they run, not what they do.
For most people reading this, email clients matter because they control how your subscribers see your emails. When you send a newsletter, you don't control whether someone opens it in Outlook, Apple Mail, Gmail, or Yahoo. Each client renders HTML differently, handles images differently, and shows (or hides) your design in its own way. That's why testing across clients matters if you care about how your emails actually look.
One practical thing worth knowing: desktop clients sometimes cache images or use their own proxies, which can make open tracking less reliable. Apple Mail, for example, pre-fetches images even if the recipient never opens your email. That's not a bug. It's a privacy feature. Just something to keep in mind when you're looking at your stats.
And if you want to understand the full picture of how email gets from you to someone's inbox, start with what happens when you press Send. Or check out the difference between email clients and webmail if you're still fuzzy on where the line is.
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