A mail server detects if an incoming message is addressed to multiple recipients, in which case redundant data storage is reduced. A single shared copy of the message is stored, and a reference message, which refers to the shared message, is provided to the addressed recipients. A record of the number of existing reference messages is maintained, and decremented as each reference message is deleted by recipients. When no reference messages remain, the shared message is also deleted. A record of recipients authorized to access the shared message is also maintained, and updated as recipients delete their reference messages.