DNS records added via the DNS Manager section of the Control Panel take effect only when the domain name uses the DNS service of your hosting account.
To add a MX record, you should:
Go to the DNS Manager section.
Click on the Create button to the right of the interface.
Fill in the following fields:
Subdomain: Type the name here (e.g., "www" for www.example.com). Leave blank for example.com. Domain: You can choose to apply the changes to one or more domain names through the Domain selector. Type: Choose MX from the drop-down menu. Mail Server: Type in the hostname of the mail server (e.g. smtp.google.com). Priority: The default value is 0. MX record priority determines the order in which mail servers are tried for email delivery, with lower numbers being attempted first. TTL: This is the time-to-live value of the record. The default is 14400 seconds. We would recommend leaving the default in most cases.
After applying all values, click on the Submit button.