Can One email be on different domains?

Hi AppuSamy, the same email address can be added to multiple Zendesk accounts (on different domains) and having completely separate roles and experiences.

Hi, AppuSamy – 

There are a few things at play here, so let me define some terms to help make this clearer. 

When you use Zendesk, you have an "Instance" of Zendesk (sometimes called an "account"). Your company may have more than one Instance of Zendesk. Each one has an account ID, and represents a unique tenant with its own data store. No data is ever shared between Instances, so a user record in account ID 12345 will never have any relation to a user record stored in account ID 12346, even if they have the same identifiers (email address, phone number, etc). 

Each Zendesk Instance also has one or more "Subdomains". Most have only one, but if you use the multibrand feature, you may have more. A user record is shared between multiple branded Subdomains within the same multibrand Instance, but if you are talking about two separate Instances each with their own Subdomain, then the user record would not be connected. 

I will assume that you are talking about two separate Instances of Zendesk, and say that there is no connection between the user record in each Instance. The user can have interactions with each one separately (create tickets, send messages, comment in the Help Center, etc).

Let me know if there's something more you want to understand here, or if that answers your question. I'm not sure if you want to have a shared user between two Instances, or if you are satisfied with the same person having separate interactions in multiple accounts.