It's because it doesn't move email by email to alt storage, but the
whole file. So the emails move as is, be them compressed or
uncompressed.
I think you could do what you want, but passing the correct options,
but I don't think it would be easy to do.
I would just store them compressed all the time, saves disk space, io
bandwidth, and if it goes over the network, actually will give a huge
performance improvement.
I have moved all mine to zstd currently, from gzip I had been using
since it was possible.
Quoting Alex King alex@king.net.nz:
Using 2.3.13 (89f716dc2) (debian package), with mdbox storage.
I considering adding the zlib plugin. I understand that reading
mail can cope with either compressed or uncompressed mailboxes.I'm wondering if I can leave the main storage uncompressed, while
having the alternate storage compressed. There does not seem to be
a way to configure this, from
https://doc.dovecot.org/settings/plugin/zlib-plugin/ it seems
compression (on saving emails) is an all-or-nothing option?Can I leave zlib_save unset in my main configuration, and have
doveadm use some alternate configuration with zlib_save set? It
doesn't look hopeful because I don't see the ability to use a
different config at https://wiki.dovecot.org/Tools/Doveadm/Altmove.Perhaps I would need multiple copies of the daemon running?
Or is it better just to compress everything? I plan to store older
mails (perhaps 3months+) in the alternative storage, and was
thinking it would be nice to have those compressed, while I don't
need to compress the main store.Any feedback welcome.
Thanks, Alex