domain name system - DKIM check=pass but DomainKeys check=neutral

I got it to set up DKIM, I sent a test mail to check-auth@verifier.port25.com and reply was :

SPF check:          pass
DomainKeys check:   neutral
DKIM check:         pass
SpamAssassin check: ham

looks good, but why DomainKeys check just neutral ? in the mail-header I see the DKIM-signature, is that a big problem that its just neutral ? how to fix that ?