diff -up dovecot-2.0.beta4/doc/example-config/conf.d/10-mail.conf.defconf dovecot-2.0.beta4/doc/example-config/conf.d/10-mail.conf
--- dovecot-2.0.beta4/doc/example-config/conf.d/10-mail.conf.defconf	2010-03-25 15:13:01.458494067 +0100
+++ dovecot-2.0.beta4/doc/example-config/conf.d/10-mail.conf	2010-03-25 15:13:01.459364459 +0100
@@ -262,6 +262,7 @@
 # them simultaneously.
 #mbox_read_locks = fcntl
 #mbox_write_locks = dotlock fcntl
+mbox_write_locks = fcntl
 
 # Maximum time to wait for lock (all of them) before aborting.
 #mbox_lock_timeout = 5 mins