Related Clues:

• Online memo
• Place for an emoticon
• Call alternative
• Cyberspace note
• Correspondence sans stamp
• It doesn't leave a paper trail?
• Virtual inbox fill
• It may come with attachments
• Target of some filters
• Forward, perhaps
• Where all addresses include @
• What a server may serve
• Letters that can arrive at any time
• Write, these days
• Office communication