[Mimedefang] action_replace_with_url

David F. Skoll dfs at roaringpenguin.com
Mon Nov 12 20:32:05 EST 2007

Roland Pope wrote:

>>> We use cyrus-imapd and 'singleinstancestore' to deal with the issue
>>> of large attachments sent to multiple users as it creates one file
>>> and hardlinks all the copies into it.
>>> Overall, on our mailserver is has saved us around 20% of disk space.
>>> Can be an issue though if your backup software doesn't restore
>>> hardlinks and you have to reload the whole filesystem :)


> The store doesn't care if the users are POP or IMAP, it does the
> hardlinking on delivery and only deletes the single copy when it has no
> more references, so yes, it does work for POP.
> There are conversion scripts that will take you from MBOX format to
> Cyrus-IMAPd if you are keen to move.

Cyrus IMAP is a wonderful piece of software, but be aware of two things:

1) It has a fairly steep learning curve and is designed to run on
a "sealed" server.  So Cyrus user-accounts don't necessarily have
anything to do with UNIX user accounts.

2) Unless things have changed since I last used Cyrus, the
single-instance store will not recognize identical messages unless
they have the same Message-Id.  So if some silly person sends 100
copies of an attachment in 100 separate messages, I don't think the
single-instance store buys you anything, whereas
action_replace_with_url does (because it keys off a hash of the
attachment content.)



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