Unfortunately I inherited an Active Directory domain whose name is a DNS name the company does not own - we'll call it ABC.com. I would like it to be something under company.com instead (per MDMarra's answer on AD naming I'd probably use ad.company.com since you never want to use a DNS name you use for anything else), but the hard requirement for now is to be able to move email to Office 365 this year and using Directory Synchronization. For that, it looks like at a minimum I need a matching UPN to our email domain (company.com). Ok, the process for adding a second UPN seems simple enough. Testing it and moving accounts over until they are all on the desired UPN seems reasonable enough.
Is there any downside to just doing this? Will the technical debt grim reaper eventually arrive if we stay on this 'non-owned' domain name of ABC.com indefinitely?
For reference, we have a single forest, single domain with everything (forest, functional level, all DCs) at 2012R2 level and Exchange 2010 on this domain. There are around 150 users and 450 computers in AD (lots of dev/test automation). While I've safely navigated us from 2003 forward to 2012R2, I would by no means call myself an expert at AD.
It doesn't look like domain renames are generally advised, and since we have Exchange 2010 on our domain I don't believe it would even be an option.
As I see it, I could either:
- add a second UPN and be done. I can deal with having to manually set the UPN on things as we create/add them...
- add a second domain to the forest, move everything over, and always have this legacy root domain forever that I can't remove
- create a second forest, forest <-> forest trust, do everything the way I really want it on this new forest from the ground up...move everything, and eventually remove the original forest. Really slow, really carefully, tested forwards and back, and probably at great expense (at a minimum in time spent). In a dream world this seems best, but I am not sure I can justify a business case for this (unless someone states a grim reaper arrival will occur).
- ??? something else I haven't thought of