Mac OS X v10.6.2 and later changes how authentication works for receiving POP messages in Mail. Mail no longer will try a different authentication method if the preferred one did not work. This means if your POP mail server does not support the authentication scheme you have selected in Mail preferences, Mail will be unable to process incoming messages.
Ensure you have selected the appropriate authentication scheme selected in Mail preferences:
- Open Mail if it isn't running.
- From the Mail menu choose Preferences.
- Click Accounts.
- Select your affected POP account on the left side.
- Click the Advanced tab on the right side.
- Choose the correct authentication method from the pop-up menu. Contact your ISP or mail provider to determine what the correct settings should be if you don't know: Password, MD5 Challenge-Response, Kerberos Version 5 (GSSAPI), Authenticated POP (APOP), or NTLM. If you are affected by this issue, try Password or APOP first.