[Dovecot] Custom Headers/Flags Support in dovecot

[Ramesh Natarajan]

I am currently trying to evaluate if I can use dovecot to be used for my
imap server like application. This is not an email application but a
generic storage server that uses IMAP protocol to save and retrieve
messages.

The messages have standard From/To/Date headers and a lot of custom headers
for threading conversations e.t.c.  As a part of my application
requirements I also need to support custom flags and have ability to
set/change/retrieve them via IMAP.

1) Does Dovecot support custom flags to be set/changed/retrieved?
2) I understand dovecot optimizes standard RFC822 headers and flags in
cache/index files for faster lookups and searches. Does custom headers and
flags fall into this optimization algorithm?
3) I am planning to support multiple users and each mailbox may have upto
1000 folders.  Each folder may have an average of  20 MIME encoded
messages. I am planning to use local storage with single-dbox format. Do
you see any issues with this?

thanks
Ramesh