How to find out if email address is team member?

I want to know if it is possible to check through the (basic) API whether a given email address is a team member or not.

 

My case is the following:

I want to let people share files through our own app. When the active user has Dropbox Teams and sharing files externally is turned off, I would like to detect whether a 'Share' operation will work before actually performing it. For this I would like to check the email address of the recipient that the user has specified. If the recipient is a Team Member, sharing is allowed. Otherwise a message is shown and sharing is not allowed.

 

I figured out how to check if external sharing is allowed, by checking the SharingPolicies for the active account. I get the active account using 'Users/GetCurrentAccount'.

 

If I could get the AccountId for the recipient, I could call 'Users/GetAccount' which should tell me whether it is a Team Member or not. However, I don't know how to get the AccountId for a given email address.

 

Can someone tell me how to get the AccountId for a given email address, or if I could use a different approach to check whether an email address is a Team Member?

 

NOTE: I would like to avoid using the Business API.