I have two email accounts hosting two separate custom domains. These where setup a long time ago and are both grandfathered on the free mail plans. I will be upgrading my primary domain soon and would like to merge the second domain into the same universal login. What is the process for this? Should I upgrade the core account and then contact support to merge the other domain in? Do I need to upgrade both plans and then contact support? I don't think there is a way to merge both existing account on the user end.

Thanks,