When an outbound email is generated from a Conga® HTML Email Template, SendGridSendGrid® is enabled, or when merging multiple documents, Composer® automatically assembles the email and presents the Conga Email User Interface. If none of those conditions are met, the standard Salesforce Email Task screen is used when emailing a Composer generated document.
You can customize the formatting and delivery options before sending the email using the Conga Email User Interface. You can also make these customizations using Composer Email Parameters.
Composer will automatically change the "Related To" value to the master object record when the email is sent so that the resulting completed Task is associated with the master object record. The default "to" recipient is also the Related Contact on the Composer User Interface (typically the Primary Contact on the master record).