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AFAIK, Google mail servers (gmail) can detect duplicate files. For example, if you receive a big file as attachment that exactly exists in someone else's inbox, google avoids storing the file twice, but instead it will make pointers to the same file.

This is a great feature. For instance, if a file is K MB and is stored by U users in their inboxes, it will be stored once, and ( (K-1) * U ) MB will be freed.

I am wondering if there is any open web-server application that supports this feature.

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  • I guess your equation should be K * (U-1)
    – bers
    Nov 18, 2016 at 14:41

1 Answer 1

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Dovecot supports attachment deduplication (under the name "single instance storage") when using the mdbox storage format, since version 2.1. You'll need these settings in 10-mail.conf:

mail_attachment_dir = ...
mail_attachment_min_size = 128k
mail_attachment_fs = sis posix
mail_attachment_hash = %{sha1}

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