An e-mail system is disclosed that overcomes many deficiencies of, but is backward compatible with, existing e-mail systems. Embodiments of the system may include various features, including but not limited to: (1) secure transfer of e-mail messages, without the need for users to replace existing e-mail clients or to change e-mail addresses; (2) tracking of all actions performed in connection with an e-mail transmission; (3) the ability for a recipient to view information about an e-mail message, optionally including information about how other addressees have responded to it, before deciding whether to retrieve the e-mail message; (4) the aggregation of entire e-mail conversations into a single threaded view; (5) the ability to include both private and public messages in a single e-mail communication; (6) sender control over downstream actions performed in connection with an e-mail message; (7) flexible control over cryptographic methods used to encrypt emails messages for storage.