If you wish to use a remote Mailserver, a few changes will need to be made.
1)?Go to User Panel -> domain.com -> MX Records
There should be an option for "Local Mail Server". ? Uncheck that option.
2)?You'll need to change the MX dns record to point to the external mailserver. ? Remove the "mail" MX record and add "other.domain.com." as the new MX record where that is the domain of the other server.
** If you do not have the MX Records menu in your DirectAdmin User Level login, then ask your hosting provider to enable the DNS Control option for your account.