[Dovecot] Converting mbox to Maildir, all prior read messages are downloaded as new

[Eric and Barbara Sammons]

I am running dovecot 0.99.  Everything works great; however, now I am 
looking at several different tools to convert mbox to Maildir.  It seems 
the tools, mb2md.pl, perfect_maildir.pl, and others all do what they 
claim; however, when the messages are converted and they are stored in 
Maildir/cur, the email clients download these messages as new.

This typically wouldn't be a problem; however, I am dealing with 100s of 
users with 1000s of emails and this really isn't acceptable behavior to 
them.  Any thoughts on how to correct this issue and prevent the client 
from downloading these messages again?

As a note, my test client is thunderbird and my preferred mbox to 
Maildir tool is mb2md-3.20.pl. 

Thanks!