Apple

Error: Could not connect to this POP/IMAP server. Check your network connection and that you entered the correct information in the Account preferences.

Error: The account "_____" appears to be offline due to a network problem. Do you want to try go online now?

Error:
Unable to Receive Mail
The mail server denied access to the account "______" because an administrator or other mail client was using it when Mail tried to log in. Try again later.
The server returned an error: account is locked by another session or for maintenance, try again.

1. Click on the Mail menu at the top left of the screen and select Preferences
2. When the Preferences window appears, ensure the Accounts tab is selected.
3. Select the account from the left column that Connection Doctor displayed the error for.
4. Under the Account Information tab on the right, update the username and password fields halfway down the page.