customconfig.pm and mailwatch 0.3

[kfliong]

I just upgraded to lastest mailscanner. I now need to upgrade mailwatch
from 0.2 to 0.3.

The problem is mailscanner created a new file CustomConfig.pm.rpmnew. So,
which file do I update for 0.3? Do I use the new one from mailscanner or
the old one from mailwatch 0.2? Or I need to do some custom changes that
merge both?

BTW, can I know what is this CustomConfig.pm file for?