You only want to use on-premises servers to authenticate. You would like to allow access to cloud email accounts through a user's local credentials. Which solution should you use?

You only want to use on-premises servers to authenticate. You would like to allow access to cloud email accounts through a user's local credentials. Which solution should you use?

• Implement SaaS
• Recreate user accounts in the cloud
• Replicate local user accounts to the cloud
• Identity federation 

EXPLANATION

Identity federation uses a single identity provider to authorize user access to multiple software applications, including cloud email.
Replicating user accounts means you are NOT using the on-premises user identities as you require. SaaS provides end-user software services over the network and has nothing to do with authorization. Recreating user accounts in the cloud won't work because we need to use local user accounts for authentication.