Keep apprised, in a way

• Email sending option: Abbr
• Covert message inclusion
• Include in an email secretively
• Emailing option
• Include invisibly in an email
• Secret attachment, for short
• Discreet email letters
• Secretly address an email to: Abbr
• Include in the email secretively

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