mailgroup is an email address that redirects to multiple email addresses. It is not an email list and should never be used in place of a real email list which is a service that we do not provide. If you want to setup an email list, here are some options.
Here are instructions on how to create a mailgroup for your site:

Log in to your control panel.
Select the domain name that you want to apply the change to.
Click on MAIL.
Enter the mailname that you want to create (ie. "joe", not the full address).
Click on ADD.
Check the "Mailgroup" box.
Click on ADD.
In the new window that opens up, either enter external recipient email or one of email accounts associated with your domain.
Click on ADD.
Repeat this for each destination address.
Click on UPDATE.