I am working on a project where a new MS Exchange 2016 will be installed on a new server for a company. The company has already a working AD with 700 users and decided to buy and setup an Exchange server. Because I do not want to mess-up with the existing servers, I prefer to setup a new machine, join in to the AD, deploy Exchange etc.... I have read a few tutorials on this, I tested it in a virtual lab but I would like to know whether this setup is going to harm/modify something on the working AD. Has anyone deployed an Exchange server by joining the machine in an existing AD? Additionally, is there a better design concept instead of mine, when creating an Exchange for an existing AD? (e.g. create a new domain only for mail purposes_.
Thank you very much for your time.
To answer your questions (but if I were you, I wouldn't do these tasks without an MS Exchange architect in your project team).
1st point: If you join an MS Exchange server to an existing ActiveDirectory where no MS Exchange server was installed in, you need to run a process called "Schema Update". This will adjust the whole AD schema and will add additional fields which are required in order to run an Exchange server. If they already have an Exchange Server (e.g. 2010) and you wish to install Exchange 2016, you need to upgrade the schema via the Exchange 2016 installation.
By the way, if the AD schema is also very old because they are using Windows NT (which I really hope not, but such stuff happen sometimes), you need at first upgrade the normal AD schema before you can prepare that for Exchange. Exchange 2016 required that the functional level of your forest is at least Windows Server 2008, and that the schema master is running Windows Server 2008 or later as written here.
Also make sure you have an AD backup if something breaks during that process!
2nd point: You might setup a different/own domain only for the Exchange server and then build some trusts between the domains. But this setup would take some additional work and also require somebody to administer the 2nd domain!