Possible Clues:

• Includes, electronically
• Shares written threads with
• Hypodermic needle amts
• Loops into a conversation, briefly
• Keeps in the loop, in emails
• Spreads threads
• Adds to an email chain, in a way
• Keeps in the loop, email-style
• Includes in an email: Abbr
• They're found below the "To" field