Hi Timo,
One thing that concerns me right now about my main clients site that I will soon be migrating from courier-imap to dovecot is the message/thread a while back about the problems with SIS and backups. I am trying to decide between using dovecot's SIS, or using mimedefang's ability to replace attachments with hyperlinks to them (storing them on a webserver - still not clear on exactly how it works or the security implications of doing so). It looks like using mimedefang would eliminate the problem with backups, and would provide the added benefit of eliminating large file attachments for external recipients as well, however I'm concerned about security - ie, how do you limit access to these attachments to only the recipients of the message with the hyperlink in it?
Anyway here is the thread outlining the problem with dovecot's SIS and backups:
http://www.dovecot.org/list/dovecot/2011-December/062340.html
Have you given this any more thought?
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Best regards,
Charles