Returns the SMTP send-option config stored for the given API key. Returns a 404 if you haven't set a config for that key — the key still accepts SMTP submissions, using your organization's default pool, the transactional category, and tracking on. ID of the API key this config applies to, the same key your SMTP client authenticates with. One config exists per key. ID of the IP pool that SMTP sends with this key use, or `ipp_shared` for the shared pool. `null` when this key uses your organization's default pool. Content classification applied to messages submitted over SMTP with this key. Controls suppression policy: `marketing` blocks on all suppression reasons; `transactional` allows delivery through complaint and unsubscribe suppressions. Possible values: `marketing`, `transactional` Structured `{name, value}` labels applied to every message submitted over SMTP with this key — the same tags used by the email sending API. See EmailMessageSendRequest for how tags are used for filtering and analytics. Tag name. ASCII letters, digits, underscore, and hyphen only. Case-sensitive. Maximum 32 characters. Tag value. ASCII letters, digits, underscore, and hyphen only. Case-sensitive. Maximum 64 characters. Whether open events are tracked for messages submitted over SMTP with this key. Whether click events are tracked for messages submitted over SMTP with this key.