[Dovecot] Dovecot / OS X 10.4 Mail.app and "Too Many Opened files" error message ?

Hello,

I am trying to move from Courier-imap to dovecot....

Even if the processes to move logical (eg name spaces etc...) went
very and without any problem, I've some etrange behavior when Imap
client is Mac OS X Mail.app.

I've got a big mailbox that have about 3 / 4G of mail in several
folder (lots !!!)...

After a long time, the OS X client say error : "Too Many opened files".

I have check on the servers (a FreeBSD farm of 3 servers using
freebsd ports of dovecot)...

And nothing special...

A question : why do I have never this kind of message on courier imap
and why do I get this on dovecot... ?

Configuration file on demand... if needed...

THanks, /Xavier