dovecot: create junk folder automatically

dovecot/files/filter_junk.sieve

 require "fileinto";
 
 if header :contains "X-Spam-Flag" "YES" {
-  fileinto "Junk";
+ fileinto :create "Junk";
 }
 
 if header :contains "Subject" "*SPAM*" {
-  fileinto "Junk";
+  fileinto :create "Junk";
 }