diff --git a/modoboa_installer/scripts/files/dovecot/conf.d/10-auth.conf b/modoboa_installer/scripts/files/dovecot/conf.d/10-auth.conf
index b6d3283..d991a50 100644
--- a/modoboa_installer/scripts/files/dovecot/conf.d/10-auth.conf
+++ b/modoboa_installer/scripts/files/dovecot/conf.d/10-auth.conf
@@ -47,7 +47,7 @@
 # the standard variables here, eg. %Lu would lowercase the username, %n would
 # drop away the domain if it was given, or "%n-AT-%d" would change the '@' into
 # "-AT-". This translation is done after auth_username_translation changes.
-#auth_username_format = %Lu
+auth_username_format = %Lu
 
 # If you want to allow master users to log in by specifying the master
 # username within the normal username string (ie. not using SASL mechanism's