Calendar invitations are issued by the 'calendaring system' within Mailtraq on behalf of the User.
The return address used follows the Server Domain name entered in the Console.
In some environments users may be using Domain Aliases or external email addresses as the return address in their email clients.
It is recommended that the default setting is not changed, to ensure that invitation confirmations are correctly routed.
Mailtraq does allow (from build 2718) the Administrator to change the default address to a custom setting in the Mailtraq Console.