To send an email blast to a specific type of recipients in your org, please create views with filters as per your requirement.

The filters can be anything related to the selected object. For example, if you want to send an email blast to Contacts then the filters for the views can be added to Contact type, Billing Address, Contact related to a specific account, etc.,

Once the view is created in Salesforce you can select that view and send an email blast using the PK4Connect application.