Rsync snapshots, Maildir, and Sarbanes-Oxley

[jabr at gapps.blu.org (John Abreau)]

Another issue I'm thinking about for my rsync backup server concerns
users' Maildirs. My mail server runs Courier IMAP, with incoming mail
dropped into Maildir mail folders. As I understand it, Maildir stores
message metadata in each message's filename, and that suggests
that Maildirs could chew up a lot of space on the rsync server with
redundant copies of the same message in slightly different filenames.

For Sarbanes-Oxley purposes, I need to retain all messages, so
I can't use rsync's --delete option to remove messages from the
backups that the user had deleted. But I suspect that means the
backups will contain multiple copies of the same message with
different filenames, and I imagine that would screw things up when
I need to do a restore.

How are others handling this sort of issue? Is there a simple way
to avoid having duplicate copies on the backup server?

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