Get a MX record to point to your FQDN (fully qualified domain name, something like mail.my-company.com)
Contact the person in charge of your nameserver to request this change.
If that happens to be you, here is what the record looks like in a bind zone file:
Code:
my-company.com. IN MX 10 mail.my-company.com.
Nope: You must have a fqdn.