[Dovecot] Unique message IDs?

[Alexander Chekalin]

Hello,

I'm working with indexing my mail box. What I need is to have index in 
which mailing specified header string is located. I work with the 
messages via IMAP. I know that sounds like FTS can help me but no, I 
don't want to index whole message nor I want to patch FTS source to make 
it to index headers only.

I need a way to identify message across my mail box. The idea is that I 
can move messages between IMAP folders and the index still should be 
able to identify it.

What I want to know, will UID strings be unique across all my messages 
no matter which IMAP folder it belongs now to, or the UID can change if 
I move message? If I remove dovecot-uidlist from the folder will UIDs of 
messages in the folder be changed? What happened if I put a message to 
the given IMAP folder (and dovecot-uidlist will record UID for it), then 
shut down dovecot, and (given maildir storage model) move the message's 
file info another folder in the same mail box - after I start dovecot, 
will the UID for the message be the same or not?

Thank you in advance,
   Alexander Chekalin