Include covertly in an email

• Send covertly, as a dupe email
• Secret attachment, for short
• Discreet email inclusion
• Discreet email option
• Private attachment, briefly
• Privately include in an email: Abbr
• Email add-on
• E-mail abbr
• Include in an e-mail without other recipients knowing

Wiktionary Word definitions in Wiktionary
init. 1 body-centered cubic 2 blind carbon copy vb. to send something by blind carbon copy