Brother MFC-8640D - Manual (Page 80)

USING CONTROLCENTER2.0 4 - 8
E-mail
Scan to E-mail feature allows you to scan a document to your
default E-mail application, so you can send the scanned job as an
attachment. To change the default E-mail application or attachment
file type, right-click on the button and select Software Button.
To change the E-mail application, select your preferred E-mail
application from the E-mail Application pull down list. You can add
an application to the list by clicking the Add button. An application
can be deleted by clicking on the Delete button.
You can also change the other settings used to create the file
attachments.