Use when working with the Gmail API on Google Cloud — OAuth2 setup, service accounts, scopes, listing and reading messages, creating drafts, batch requests, and quota handling. WHEN: gmail api, google workspace email, read my inbox programmatically, create a gmail draft, gcp oauth consent screen, gmail api quota exceeded, refresh token expired. DO NOT USE FOR: sending mail via SMTP relays, Google Calendar or Drive APIs, or non-Google mail providers.