Automated message to user phone while registering or after placing the order isnt with the name of my domain name but its with name of some DM_MSTORE?

StoreHippo has an account with SMS provider to send automated SMS for the respective events, by default all the SMS to users and admin are sent through StoreHippo's default SMS provider, hence it is sent in the name of DM-STORE which is the registered name of StoreHippo with the SMS provider.

You can also set up your own custom SMS provider to start sending the SMS from your own sender name.