* @param discloser the mail posting discloser
     */
    protected void sendToSlack(final CardView cardView, final SMailPostingDiscloser discloser) {
        // https://api.slack.com/messaging/webhooks#posting_with_webhooks
        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        final String slackWebhookUrls = fessConfig.getSlackWebhookUrls();
        if (StringUtil.isBlank(slackWebhookUrls)) {

- **Admission webhooks:** Admission webhooks are in widespread use as a Kubernetes extensibility mechanism and have been available in beta since the 1.9 release. The 1.16 release marks the graduation of admission webhooks to general availability (GA).

Kubernetes 1.19 / go 1.15. Serving certificates used by admission webhooks, custom resource conversion webhooks, and aggregated API servers must now include valid Subject Alternative Names. If you are running Kubernetes 1.22 with `GODEBUG=x509ignoreCN=0` set, check the `apiserver_kube_aggregator_x509_missing_san_total` and `apiserver_webhooks_x509_missing_san_total` metrics for non-zero values to see if the API server is connecting to webhooks or aggregated API servers using certificates that will be considered...

* The webhook admission plugin now works even if the API server and the nodes are in two separate networks,for example, in GKE.
The webhook admission plugin now lets the webhook author use the DNS name of the service as the CommonName when generating the server cert for the webhook.
Action required:

- Fixed an issue where the API server did not send impersonated UID to authentication webhooks. ([#116681](https://github.com/kubernetes/kubernetes/pull/116681), [@stlaz](https://github.com/stlaz)) [SIG API Machinery and Auth]

- Kube-apiserver: Authorization webhooks now report the following metrics:
  - apiserver_authorization_webhook_evaluations_total
  - apiserver_authorization_webhook_duration_seconds

- APIServerTracing now collects spans from outgoing requests to admission webhooks. ([#103601](https://github.com/kubernetes/kubernetes/pull/103601), [@dashpole](https://github.com/dashpole)) [SIG API Machinery]
- Add a namespace label for all `apiserver_admission_* metrics`.

- Added the ability to host webhooks in the cloud controller manager. ([#108838](https://github.com/kubernetes/kubernetes/pull/108838), [@nckturner](https://github.com/nckturner))

- Kube-apiserver: timeouts configured for authorization webhooks in the --authorization-config file are now honored, and webhook timeouts are accurately reflected in webhook metrics with result=timeout ([#125552](https://github.com/kubernetes/kubernetes/pull/125552), [@liggitt](https://github.com/liggitt)) [SIG API Machinery, Auth and Testing]

- Added a new metric `webhook_fail_open_count` to monitor webhooks that fail to open. ([#107171](https://github.com/kubernetes/kubernetes/pull/107171), [@ltagliamonte-dd](https://github.com/ltagliamonte-dd))