In order to host your domain at one place, but use a remote mail server you only need to add/edit your MX record. Below is an example on how you can do that via Cpanel (note that the steps should be similar with most control panels).
1. Login to your Control Panel.
2. Click on the DNS zone and add the MX record, in our case this is achieved by clicking the MX Entry under Email.
3. Under Add New Record, you can type the priority and destination of the new mail server to which you wish to point the domain.
Destination: The hostname to which you wish to point your mail server.
Priority: Priority numbers indicate the order in which the mail servers should be used, this enables the use of primary and backup mail servers.
Note: If you already have a MX record with priority "0" you will need to remove it in order to set the new MX record.
4. When you are ready click Add New Record and after the DNS propagate you will be using the remote mail server.