Thanks, Robert,
will take a look at.
What I'm afraid for is how database storage should be planned (storage, CPU, RAM, scaling when will be over-filled). When dealing with files (I'm using maildir), it is much easy to understand and to fix just about everything. Adding database involves tune it up too, and I'll have more points of 'tune it a bit'
In fact work with Dovecot is pretty nice, but I think I can tune it to work faster.
I now run it on FreeBSD (on UFS2), maybe I should change OS + FS, but need to test (really hope ZFS disks on SAS drives will help; still find no benchmarks on such a setup). Will also try to use full text search, but afraid of index size (and I need no search on body, just on headers).
Anyway thank your for pointing me in right directions!
Yours, Alexander