Apple's Mac OS X operating system comes with the Apple Mail client included with the system. The Apple Mail client is considered a traditional email client. This means it can connect to both POP3 and IMAP email servers to send and retrieve messages from an email account. The Apple Mail client, like most other applications on a Mac OS X system, is capable of starting automatically when the computer boots. This can be disabled through the Finder.
Boot the computer completely into Mac OS X.
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Hold the "Ctrl" key on the keyboard.
Click the Apple Mail icon in the Dock while still holding the "Ctrl" key. A context menu appears. Release the "Ctrl" key after clicking.
Move the mouse pointer over "Options." This presents a sub-context menu.
Click "Open at Login" to uncheck it. The context menu automatically disappears after you click. The next time Mac OS X boots, the Apple Mail client will not start automatically.