On the Accounts Settings box, select More Settings. Select your Redtail hosted account then select Change or simply double-click the account. Using a POP account on multiple devices will require you to delete email on each device (if you've opted to leave a copy of the messages on our server).
It is best to only adjust this setting to retain messages for a short window rather than indefinitely, which can pose issues. By default a POP account removes the emails from our server after delivery, but you can adjust your server settings before or after establishing the account to opt to leave a copy on our server.