Google announced that it is changing the way that delegate settings are managed within G Suite. The Gmail API is being expanded to handle these settings, and the Email Settings API, which had previously been used for controlling delegate relationships, will be deprecated as of October 16, 2019.
Google has released an updated Gmail API that functionally replaces the Email Settings API. The Gmail API includes a number of new endpoints that enable features previously unavailable through any Google API. Developers have access to filters, auto-replies, send-as aliases, and more.