Naming new AD domain same as UPN suffix in old domain & O365 integration

Will adding a UPN suffix to our current DomainName.local AD environment create an issue if we eventually create a new AD environment with the Forest/Domain name of the newly added UPN suffix?

Example:

Current AD Environment:
Current AD domain:  DomainName.local
Current Exchange account email domain: mail_user@cityname.gov
Current website/webpages (*externally hosted): cityname.gov or www.cityname.gov
Current AD OS Environment: 2008R2
Exchange version: 2010

O365 requirements:
routable domain name options: domain.com, domain.net, domain.gov

O365 suggests adding a UPN suffix with routable domain extension to current environment (Example: New UPN suffix: cityname.gov)

We will be redesigning/creating a new AD environment several months down the road. We want to name the new domain: Internal.CityName.gov

1. With our current environment, should I add the following UPN suffix: cityname.gov and/or internal.cityname.gov?

2. If we add internal.cityname.gov as a UPN suffix to our current environment, what issues might I face if we set our new AD domain name also as internal.cityname.gov?

3. Should I only add ‘cityname.gov’ to our current AD environment to start our AD domain with the connection to O365?
LVL 4
Gene BlakeSenior Systems Engineer IIIAsked:
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timgreen7077Exchange EngineerCommented:
You can add the suffix. once you redesign your environment you can remove the suffix and setup the new domain with that name. adding the suffix will not cause any issues.
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Seth SimmonsSr. Systems AdministratorCommented:
No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I have recommended this question be closed as follows:

Accept: timgreen7077 (https:#a42472131)

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