The machine receiving the I-fax can send an MDN to the IP address of the sending machine without going via a mail server. An MDN is a notification e-mail for checking the sending result.
1.
Press 
(Settings/Registration).
(Settings/Registration).2.
Press [Function Settings] → [Send] → [E-Mail/I-Fax Settings].
3.
Press [Allow MDN Not via Server].
4.
Press [On] → [OK].
Select [Off] to always send the MDN (Mail Delivery Notification) mail via a mail server.