Sharp Version 2.5 - Manual (Page 20)

RightFax MFP Module 2.5 Guide for the Sharp Extension 20
7. Click the Destination tab.
Figure 2.3 Setting Certified Delivery as the default send method
8. Select the option Certified Delivery.
Tip Selecting the Force Send Type option on this dialog box will
prevent other types of document transmission from functioning. If you
select Certified Delivery or SecureDocs and this option is checked,
documents sent to fax numbers will fail.
9. Save the changes and exit.