fs-compress plugin

It can be used by any of the settings using the FS drivers (e.g. obox_fs, fts_dovecot_fs, etc.)

The exact location where to set it in the FS driver string depends on what other FS drivers are being used.

The important rules are:

  • Must be set before the final storage driver (s3, sproxyd, …)

  • Should be set after fscache (you generally don’t want fscache to be compressed for performance reasons).

  • Must be set before fs-crypt and fs-mail-crypt, because encrypted data compresses poorly.


See fs-compress plugin for dovecot.conf setting information.

The fs-compress configuration format is:


See zlib_save for information on available compression algorithms.

See zlib_save_level for information on compression levels and defaults.

Optional compression

New in version v2.2.34.

By default fs-compress requires that the mail is compressed with the specified algorithm.

To allow adding compression to existing storages without compression, you can use the “maybe-” prefix in front of the algorithm.

For example:

obox_fs = fscache:512M:/var/cache/mails/%4Nu:compress:maybe-zstd:3:s3:https://ACCESSKEY:SECRET@s3.example.com/?bucket=mails

This decompresses mails if they were stored using zstd compression and falls back to reading the mails as plaintext.


Prior to v2.3.13 it is not possible to use multiple different algorithms for the same user.

Example Configuration

obox_fs = fscache:512M:/var/cache/mails/%4Nu:compress:zstd:3:s3:https://ACCESSKEY:SECRET@s3.example.com/?bucket=mails
fts_dovecot_fs = fts-cache:fscache:512M:/var/cache/fts/%4Nu:compress:zstd:3:s3:https://s3.example.com/%8Mu/%u/fts/?bucket=mails

Note that these both work and don’t have any practical difference, because fs-dictmap doesn’t modify the object contents in any way:

obox_index_fs = compress:zstd:3:dictmap:proxy:dict-async:cassandra ; sproxyd:http://sproxyd.scality.example.com/?class=2&reason_header_max_length=200 ; diff-table
obox_index_fs = dictmap:proxy:dict-async:cassandra ; compress:zstd:3:sproxyd:http://sproxyd.scality.example.com/?class=2&reason_header_max_length=200 ; diff-table

With encryption enabled:

obox_fs = fscache:512M:/var/cache/mails/%4Nu:compress:zstd:3:mail-crypt:s3:https://ACCESSKEY:SECRET@s3.example.com/?bucket=mails