[Dovecot] Dovecot hard link problem

[Timo Sirainen]

On Sun, 2008-06-01 at 23:27 +0900, 도원철 wrote:
> My company recently changed mail server from cyrus to dovecot.
> 
> The problem is that dovecot does not support hard links for message
> files with same message ID.
> 
> I turned on the ‘maildir_copy_with_hardlinks’ option in dovecot.conf,
> but it does not seems to have relation to this problem, am I
> misunderstood?
> 
> Hard links are created when move or copy messages from one folder to
> other folder, but when deliver creates messages this option does not
> works.

Right. This isn't implemented yet. Also I don't think it should rely on
Message-ID: header proving the uniqueness. There are two ways this can
be implemented reliably:

1) If the message is sent to multiple recipients using same RCPT TO
command, all the recipients could be given to deliver as parameters, and
deliver would know that it's the same message and they could be hard
linked.

2) Keep some kind of a hash database where hash is e.g. SHA1 sum of the
entire message. All messages could be then stored in some global
directory and hard linked from there to users' mailboxes. When receiving
a new message using an existing hash, it could still compare
byte-by-byte the files to make sure that it's not a hash collision
before hard linking the file.

1) probably wouldn't be too difficult to implement and probably would
solve your problem (assuming the problem is that people are mailing
100MB attachments to everyone inside a company). But I don't think I
have time to do it myself..
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