Same user, 2 email addresses?

Same user, 2 email addresses?

If a user was setup with name@site1.com, can you add name@site2.com under the same user, but also be able to send mail depending on business needs from either one?

OR do i need to set that person up as 2 separate users?

Hopefully someone answers here. Never got an answer from sales@zoho that i sent 4 days ago.