migrating mailboxes by copying files?

[Marten Lehmann]

Hello,

since imapsync sessions take to long for our several thousand mailbox 
setup (although it's still running in the background while I'm writing 
this) I'm asking myself, if there isn't another way to migrate the messages.

Maildir does store each message in a separate file and same does cyrus. 
The accounts in cyrus are all created. Couldn't I just copy all messages 
from a Maildir to the according cyrus-folder and run a rebuild-tool for 
the mailbox after I moved and renamed the message-files? Which scheme 
does the numbering of the files follow in cyrus? Is it always increasing 
(1., 2., 3., and so on)? If there is such a tool, what is the name and 
how can I use it? I guess cyrus is rebuilding the cyrus.* files and 
updating the quota-usage?

Regards
Marten