Perhaps storing the message, attachments, etc. in an RDBMS would be a better way. Give each user a table-space with a table per folder/directory or just each user with a single table. With a decent RDBMS, storage on disk is no longer your concern. This way web, local text/gui, and remote text/gui clients could easily access the same information. There's probably several solutions out there already (with wrappers for your favorite mail clients).
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How does AbiWord relate to an "Ant"?
Perhaps storing the message, attachments, etc. in an RDBMS would be a better way. Give each user a table-space with a table per folder/directory or just each user with a single table. With a decent RDBMS, storage on disk is no longer your concern. This way web, local text/gui, and remote text/gui clients could easily access the same information. There's probably several solutions out there already (with wrappers for your favorite mail clients).