You can add the Email Via MassMailer buttons to the Opportunity Search Layouts as explained in this section in the MassMailer configuration guide

You can select any Opportunity List View from the Opportunity Summary Page and click on 'Email Via MassMailer' button to invoke Opportunity Mass Email feature.

You can send mass emails to the Opportunity Contact Roles and track the opens, clicks etc in Salesforce using this MassMailer feature.

For complete instructions on how to send mass emails to Opportunity Contact Roles & Team Members you can refer to the article at this link.