Questions about hardlinks, alternate storage and compression

Gionatan Danti g.danti at
Sat Jun 27 16:18:47 UTC 2015

Hi all,
I have some questions about hardlinks, alternate storage and 
compression. I already scanned the list for related information and I 
have an idea of how things works, but I would like to have a definite 

System spec:
- CentOS 6.6 x64
- dovecot-2.0.9-8.el6_6.4.x86_64 RPM package/version
- sdbox mail store

1) About hardlinks: when sending the same message to two different 
recipients, I see that the two u.x files are created as two different 
files. Diffing them, I see that the only difference is a single char 
(see [1] for an example). My questions are:
   a) it is possible to tell dovecot to create a single file + a single 
hardlink (linkref=2)? As other IMAP servers support that features (eg: 
Cyrus, CommunigatePro, etc) I am wondering if I missed something in 
configuring dovecot...
   b) If it is not possible, can I run a script that compare the various 
files and substitute equal ones (minus the changing line) with 
hardlinks, or it will confuse dovecot? As a side note, why the changing 
line ever exists?

2) About alternate storage and compression: actually, I use a single 
mail_location without compression. I would like to have an alternate 
storage and to enable compression on it only, leaving the main location 
without compression. I if understand it correctly, it _should_ be done 
using a command similar to "doveadm -Dv -o "plugin/zlib_save=gz" altmove 
-uu testuser sentbefore 8d". I'm right thinking that it should work? I 
will really end with a primary uncompressed mail store and an alternate, 
zlib-compressed one?

Thank you all and sorry if I did some naive questions.

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Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. -
email: g.danti at - info at
GPG public key ID: FF5F32A8

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