[MlMt] Where is message flag color information kept?

[Greg Earle]

Benny et al.,

I'm trying to migrate my mail server at work and have come across 
something I don't understand.

If I mark messages in my work e-mail account (in MailMate) with 
red/yellow/green etc., MailMate running on my home Mac and my work Mac 
correctly see the colors.

Also, if I run Apple Mail on either my home Mac or my work Mac, they 
also correctly see the colors on both systems.  This made me think at 
first that the flag color information must be in the filename if not 
metadata in the message file itself.

But if I rsync my Maildirs from my old Ops mail server (Courier) to my 
new Dev mail server (Postfix+Dovecot), both MailMate and Apple Mail see 
every flagged message on the new server as being red - all the 
yellow/green/etc. color differential/subtlety is getting lost somewhere.

I verified that the mail message files have the same exact filename, 
size and checksum on both servers - so clearly the flag color can't be 
kept in the file or the filename?

I don't get it - how do Apple Mail and MailMate know about each other's 
colors (yes I know MailMate implements Apple Mail's flag setup), but if 
you copy the message to a different server and it's correctly preserved, 
the color information is lost?

tl;dr: Where do MailMate/Apple Mail store the flag color info for each 
message?

TIA,

		- Greg