Related Clues:

• What a server may serve
• Letters that can arrive at any time
• Write, these days
• Office communication
• Virtual inbox filler
• Sends a message to, these days
• Postal alternative
• Something you click to open
• Some cell-phone messages
• Deliver spam
• Send, on a computer
• Cyber-missive
• It might have an attachment
• Inbox contents
• Books to study