Opendkim SignTable and KeyTable

As a member of PISA and ISOC HK, I occasionally need to use the email address warren@isoc.hk and warren.kwok@pisa.org.hk from my web-based email client to send outgoing emails.  However, as the DKIM signature is binded to a single sender domain only, the outgoing emails bearing the above two mentioned sender addresses can not have DKIM signature.  Fortunately, opendkim provides a SignTable which specifies which email addresses outside the default domain can be issued with signature.  Interestingly, if the SMTP server is providing email hosting to multiple domains, all email addresses of the domains can be signed.   This also reminds me of the file KeyTable which of course by its name means different domains can use different keys and selectors.    If I have time, I will try all these out to strengthen my understanding on DKIM.