Global sieve rule

[Henry]

I wish to have a global sieve rule that moves spam mail to a user's
spam mail folder.

In Roundcube I can create this rule on a user by user basis:

# rule:[Spamassassin]
if header :contains "subject" "***SPAM***"
{
        fileinto "Spam";
}

I would like to set the above as a default for all users.