Please excuse my lack of knowledge as I am learning this on the fly.
I have a windows 2012R2 Active Directory domain called mydomainname.local with 4 servers. (AD / DC, File & Print, etc)
I need to create users with mydomainname.com that I am then going to dirsync with office365.
Do I need to create a new child domain in the same forest called mydomainname.com then create my users in the child domain?