to configure servers to relay to a remote box for emails

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http://forums.cpanel.net – hi guys i really need help to configure mail server. my server is running cpanel. the site could not send any emails because the port 25 is blocked by server provider. they wont unblock port25 for emails sending but they said however i can configure server to relay to a remote box other than port25 without the need to request any changes from them. so far i already configured a smtp server from my remote box. but i still need to configure SMTP service from server to a remote box to listen on an alternative port number other than 25. could anyone help me how to finalize this step. i really app (HowTos)