docs: update infrastructure state and roadmap

docs/email.md

@@ -10,6 +10,7 @@ Email is used for:
 * User invitations
 * Notifications
 * System alerts
+* Backup reports
 * Future CI/CD notifications
 
 ---
@@ -126,6 +127,26 @@ Configured
 
 ---
 
+### Backup System
+
+Purpose:
+
+* Backup success emails
+* HTML backup report emails
+* Operational backup notifications
+
+Delivery:
+
+* Postfix relay through Gmail SMTP
+* Gmail App Password authentication
+* TLS encryption
+
+Status:
+
+Configured and validated
+
+---
+
 ## Future Applications
 
 Future services should use the centralized SMTP configuration whenever possible.
@@ -134,7 +155,6 @@ Examples:
 
 * BaGet
 * CI/CD notifications
-* Monitoring systems
 * Alerting systems
 
 ---
@@ -186,6 +206,15 @@ Verify:
 * STARTTLS is enabled
 * Port 587 is used
 
+### Backup Reports
+
+Verify:
+
+* Postfix relay is active
+* Gmail App Password authentication succeeds
+* TLS delivery succeeds
+* Backup wrapper sends the HTML report after backup completion
+
 ---
 
 ## Security Notes
@@ -201,5 +230,6 @@ Verify:
 
 * docs/secrets.md
 * docs/security.md
+* docs/backups.md
 * openproject/README.md
 * gitea/README.md