The subject that you enter here is used as the default subject whenever you do not enter a subject when sending a job.
1.
Press 
→ [Function Settings] → [Send] →[E-Mail/I-Fax Settings] →[Default Subject].
→ [Function Settings] → [Send] →[E-Mail/I-Fax Settings] →[Default Subject].2.
Enter a subject → press [OK].