Real-world case found during setup: the sending address ([email protected]) is an
alias of an existing Workspace user, not its own paid seat (a deliberate cost-saving choice).
Domain-wide delegation authorizes a real Workspace ACCOUNT, not an arbitrary alias string, so
using the alias directly as the delegated 'sub' claim would have been wrong. Added
GOOGLE_DELEGATED_USER (the account that actually owns the alias and was granted delegation) as
an optional override, falling back to EMAIL_FROM_ADDRESS unchanged when the sending address is
itself a primary account. EMAIL_FROM_ADDRESS remains the visible From: header in both cases.
Documented in docs/RUNBOOK_GOOGLE_WORKSPACE_EMAIL.md with a concrete example.
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