notifications: add documentation for system mail forwarding

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>

diff --git a/notifications.adoc b/notifications.adoc
index e8ed51b7e462b636cac736b0ec45d794e685f5e3..c7bdc5aa11763a8617e593e283813106b8f15a07 100644 (file)
--- a/notifications.adoc
+++ b/notifications.adoc
@@ -281,6 +281,7 @@ Notification Events
 | Cluster node fenced          |`fencing`          | `error`  | `hostname`
 | Storage replication failed   |`replication`      | `error`  | -
 | Backup finished              |`vzdump`           | `info` (`error` on failure) | `hostname`
+| Mail for root                |`system-mail`      | `unknown`| -
 |===========================================================================
 
 [width="100%",options="header"]
@@ -290,6 +291,21 @@ Notification Events
 | `hostname` | Hostname, including domain (e.g. `pve1.example.com`)
 |=======================================================================
 
+System Mail Forwarding
+---------------------
+
+Certain local system daemons, such as `smartd`, generate notification emails
+that are initially directed to the local `root` user. {pve} will
+feed these mails into the notification system as a notification of
+type `system-mail` and with severity `unknown`.
+
+When the forwarding process involves an email-based target
+(like `sendmail` or `smtp`), the email is forwarded exactly as received, with all
+original mail headers remaining intact. For all other targets,
+the system tries to extract both a subject line and the main text body
+from the email content. In instances where emails solely consist of HTML
+content, they will be transformed into plain text format during this process.
+
 Permissions
 -----------