Moving mail into IMAP server and the Received date

[RM]

Hi,
I'm experimenting with setting up an IMAP server to use as a shared 
resource for our project team, to serve a history of mail involved with 
the project accumulated from a number of users over some years, 
including via newsgroup and regular mail and having been sent and 
received using various mail clients.  The accumulated mail is currently 
collected in a set of folders in my Mozilla Thunderbird mail local 
folders, and I want to move it all as-is into a secured IMAP server so 
that others can search, read and deposit mail there too.
I've been experimenting with cyrus and some other imap servers which 
also exhibit this problematic behaviour: when I move the mail from a 
local folder to an imap folder under cyrus, my adjacent 
Windows/OutlookXp mail reader sorts the mail by "Received" date, and the 
date registered as "Received" is the time/date that the copy operation 
is carried out (ie: now) rather than the date that the mail was actually 
originally received.
In Linux/Thunderbird (my primary mail reader) it uses the "Sent" date to 
sort the mail, which is fine, but Outlook thinks in terms of the 
Received date and that's going to be broken by the mail copy process.
Some questions:
Is Cyrus responsible for presenting that "Received" date, as the mail's 
pure text (view source) contains no reference to that date?
Is it possible to force Cyrus to *not* recreate that "Received" date; or 
perhaps to copy the "Sent" date to the "Received" date when mail arrives 
by copying from folder to folder, as opposed to when it is received via 
the common mail delivery mechanism?
Is it possible to run a script to reset all the Received dates for a 
given set of mail (by folder location) to match the Sent date per mail?
Thanks
 Rob