A lot of spam blockers are using a whitelist with auto verify option. Is there a way to have the spam filter verify an email?

No, there is no way for the RouteFinder spam filter to verify an email. Our routefinder only provides a basic spam filter function, it is not for use with full featured mail server, spam filter and antivirus filter.

Our routefinder have very limited disk space which can NOT be used to add features for mail server application

Companies typically dedicate another applicance for full mail server functions.