Brother MFC-8820DN - Manual (Page 264)

USING THE WINDOWS ® -BASED BROTHER SMARTUI CONTROL CENTER 15 - 27
Fax setting (PC-Fax using the Brother
Fax Driver)
The MFC includes a PC-Fax driver, which allows any Windows
Application to send a Fax as simply as printing a document. The
Brother SmartUI automatically configures the Fax button to use the
Brother PC-FAX driver no user configuration is required.
The Scan Action tab is set to Application and should not be changed.
To change the PC-FAX settings click the Link Preferences button
found in the configuration tab.