Yes. GoDaddy does have limits to the number of emails you can send per day depending on the account, so make sure to check with them and make sure your account will support the email volume you are expecting to need.
Power Messenger is a domain license and allows email segmenting, so as long as you are creating the emails and sending them you can do that for any number of clients with a single license. You would only need a separate license if you were allowing your clients to create and manage their own emails.