[Dovecot] userdb syntax

Hello,

I have a question about userdb lookup when using expire-tool.

Dovecot version 1.2.15 In dovecot.conf, mail_location = maildir:/var/mail/%u:INDEX=/var/indexes/%u

I run dovecot expire-tool, target user's directory becomes executing user's one. According to wiki, userdb setting overrides mail_location.

userdb passwd { mail=maildir:/var/mail/%u:INDEX=/var/indexes/%u }

With this setting, it seems working. But, there are no examples with ":INDEX=.." setting. Is this syntax right?

Regards