Step-by-step help needed

So, I'm not an Exchange guy... but the problem I'm facing:

Two domains, no trusts between these two, only conditional name forwarding enabled, so that domainA.local can do DNS queries to domainB.local and vice versa.

domainA.local has Exchange 2000 and domainB.local has Exchange 2013. Can someone please provide some step-by-step instructions so that I can get emails going from domainB.local to domainA.local and vice versa?

Thanks in advance.