Asana accounts can have multiple emails associated to them, but getting a user from the API only returns 1 email. So which one will it return? Is there a concept of a primary email?
https://app.asana.com/api/1.0/users/me
Great question. Users typically have multiple email addresses when they are in multiple domains. If the API call has a domain context, such as GET /workspaces/:id/users the email addresses for each user will be their registered domain email for the workspace identified. This goes for querying followers of projects and tasks as they can only exist in a single domain.
However, when your query does not have a domain context, such as GET /users/me the behavior is a bit more undefined. The reply will not change from call to call unless the user has changed that email address, but there is not a notion of a "primary" email address you, as an API consumer, can apply to that response.
Hope that helps.