You can now set a new value for INBOX.spam in the directadmin.conf. This is the internal default: spam_inbox_prefix_name=INBOX.spam to add that to the directadmin.conf and adjust as needed, if you wish to use a different value. It's only used when spam_inbox_prefix=1 is set, which is when INBOX.spam applied. Simply swaps all INBOX.spam strings with the new value. The leading dot is added internally, where applicable (eg, Maildir paths), so don't add a leading dot, else you'll get 2.