On 4.1.2010, at 21.02, David Abrahams wrote:

I just discovered that dovecot supports copying messages via hard-linking. I have a huge mailbox hierarchy of existing messages that I'd prefer to store that way. Is there a simple way to transform non-hard-linked storage to hard-linked?

Not via Dovecot. But you could create a script that finds duplicate mails, then replaces them with a hard link to one of them (and preferably in a way that mails won't get lost if user happens to delete that mail at the same time).