A. Assuming you've correctly configured Exchange 2010, enabled the user to use POP3 in the Mailbox Features tab of the user mailbox (as shown here), and ensured network connectivity, the most common cause for connectivity failure is that the POP3 service isn't running.

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As is the case with Exchange 2007, POP3 is installed automatically but the actual service is set to manual start mode—it won't run until started manually. If you intend to use POP3, you should modify the service through Server Manager, Configuration, Services, and set the Microsoft Exchange POP3 service to Automatic start mode, as shown here. You can then click the Start button to start the service immediately.

Click to expand.

You can also make this change using PowerShell with these commands:

Set-Service msExchangePOP3 -StartupType automatic
Start-Service msExchangePOP3

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