[Dovecot] Quotas - per folder message limits?

[Alan Brown]

Is there any way of enforcing a Maildir per-folder message limit in 
Dovecot?

We're finding major performance hits once a threshold of files/directory 
is exceeded. This applies across all common filesystems with the 
threshold differing depending on the FS. GFS2 pretty much _STOPS_ for 10 
minutes when users put 65k+ messages in one folder...

I'm currently running 1.1.20 but looking to update (RHEL5 cluster 
installation)