Fortimail 400E Unable to Delete Domain

Hi,

I have a Fortimail 400E unit running in Server Mode and I'm failing to delete a domain. This is the error I get:

Entry is used. (entry has been used 2 times by: domain-association:names:main-domain pki:name:domain admin:username:domain report:<name>:domains mailserver:ldap-domaincheck-internal-domain mailserver:default-auth-domain domain-setting:main-domain email-migration-domain-replacement:names:local-domain) What could be causing this error? How do I eliminate it such that I'm able to delete a domain?

Thanks.