[Dovecot] Multiply mailboxes vs one huge

[Alexander Chekalin]

Hello,

as I need to store a lot of messages on my IMAP server (order of 
900K-1000K; this is an archive for some time, maybe a year or so), I see 
some "slowness" in dealing with such a huge amount. I mainly need to do 
searches like "get all messages from user1 at domain1.com to 
user2 at domain2.tld recieved between date1 and date2".

So I really interested will it be wise to

a) split all messages into several smaller mailboxes (per-month, or 
per-day, or create 2-level-structure like "month/day/")
b) use dbox (vs currently used mbox) storage scheme (I'm afraid of mdbox 
as I still not sure I'll be able to parse it by scripts later "just in 
case")

Dovecot is the latest one (2.1.3). No compression Dovecot-side, but it 
mails are in zfs volume with compression on. I ask this mainly due to my 
not fully understand how Dovecot indexes are working.

I also test another approach: to use my own index somewhere outside 
Dovecot which will store reference between emails and UIDs, and dates 
and UIDs, so I'll simple query my index for things I need. But then, 
that's exactly what IMAP index can do, so I simple slow my search  down, 
isn't it? The only reason I think about my own index is I won't use 'all 
header' as search scope, I need to deal only with From:, To:, Cc:, Bcc: 
(if any), Recieved (if nowehere else I see the from/to info), and date 
field(s) - I doubt IMAP will care for that for me.

Yours,
   Alexander