How do I join a computer onto the domain using MDT?

You will need to edit your CustomSettings :

• In deployment bench right click MDT Deployment Share
• Select Properties
• Select Rules Tab
• In [Default] add

JoinDomain=mydomain.com
DomainAdmin=username
DomainAdminPassword=passwordforusername
DomainAdminDomain=mydomain.com
MachineObjectOU=OU=Workstations,DC=mydomain,DC=com

or edit the CustomSettings.ini file found in \DeploymentShare\Control

Lastly Update the Deployment Share in (Right click and select Update) in Workbench