Currently, when SmarterMail receives an email with an attachment it will copy that email and attachment to each and every recipient’s folder. The same is true when Smarter Mail is receiving an email which was sent to an alias/distribution groups. Each message is fully duplicated to each member of that alias group.
Here's one concept I think could greatly improve the inefficient storage use of attachments:
We should separate the attachment from the email and use a public folder where all the attachments will be saved. In addition to the attachment file created in the public folder, Smarter Mail will create a corresponding "link file" which will contain a list of all SmarterMail users who are linked to that attachment. When a user wants to open the email, it will call the attachment file through a link added to the email message - which will refer to the public folders corresponding "link file" and thus the attachment.
Unless you're the last user to delete a message from your mailbox which contains a link to the attachment, it will simply remove the link from the "link file" and leave the attachment itself intact.
The only time an attachment can be deleted is when you're the last name listed in the corresponding "link file" in the public folder. Only then can the "link file" AND the attachment file be permanently deleted.
This method can be used not only on a single email transaction, but also when someone forwards the same message internally or externally. Smarter Mail should still make use of the link concept instead of recreating another copy of the file in the sent items folder.
Possibly, the outgoing spool may need to create a temporary single file copy of the entire message for spooling purposes only and not for storing.
I really thing this can be developed and this will greatly decrease unnecessary duplication of files.