Envoi — per-workspace custom SMTP relays

Envoi workspaces can now register a custom SMTP relay (host, port, credentials, from address) under Workspace settings → SMTP. Once verified, all outbound mail for that workspace flows through it instead of the platform default — useful for keeping deliverability tied to your own sending reputation, or routing through a provider you already pay for.

Per-domain overrides let you keep transactional and marketing on different relays without splitting workspaces. Credentials are encrypted at rest with a workspace-scoped key.