If you need to configure an external mail server to handle mail for your domain, do the following:
1. Go to Mail, open the Mail Settings tab.
2. Click the checkbox next to the domain for which you need to configure external mail server, click Activate/Deactivate Services.
3. Select Disable from the menu, and click OK.
4. Go to the Websites & Domains tab, find the domain name whose DNS settings you want to manage, and click DNS Settings.
5. Click the hyperlink in the Host column corresponding to the MX resource record.
6. Type the domain name of your external mail server into the Mail exchange server field. If you are running a remote mail server named ‘mail.myhostname.com’, type ‘mail.myhostname.com’.
7. Specify the external mail server priority, where 0 is the highest and 50 is the lowest.
8. Click OK, and then click Update.