Add customizable email templates and remove alert recipients

Replaced the fixed `alert_recipients` list with customizable subject and body templates for alerts and warnings. This allows for more flexible and dynamic email notifications using placeholder variables. Updated relevant backend and frontend components to support this feature.

backend/alembic/versions/0007_email_templates.py

@@ -0,0 +1,31 @@
+"""email templates and drop recipients list
+
+Revision ID: 0007_email_templates
+Revises: 0006_email_from_name
+Create Date: 2026-02-12
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0007_email_templates"
+down_revision = "0006_email_from_name"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("email_notification_settings", sa.Column("warning_subject_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("alert_subject_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("warning_body_template", sa.Text(), nullable=True))
+    op.add_column("email_notification_settings", sa.Column("alert_body_template", sa.Text(), nullable=True))
+    op.drop_column("email_notification_settings", "alert_recipients")
+
+
+def downgrade() -> None:
+    op.add_column("email_notification_settings", sa.Column("alert_recipients", sa.JSON(), nullable=False, server_default="[]"))
+    op.drop_column("email_notification_settings", "alert_body_template")
+    op.drop_column("email_notification_settings", "warning_body_template")
+    op.drop_column("email_notification_settings", "alert_subject_template")
+    op.drop_column("email_notification_settings", "warning_subject_template")

backend/app/api/routes/admin_settings.py

@@ -29,7 +29,6 @@ async def _get_or_create_settings(db: AsyncSession) -> EmailNotificationSettings
 
 
 def _to_out(settings: EmailNotificationSettings) -> EmailSettingsOut:
-    recipients = settings.alert_recipients if isinstance(settings.alert_recipients, list) else []
     return EmailSettingsOut(
         enabled=settings.enabled,
         smtp_host=settings.smtp_host,
@@ -39,7 +38,10 @@ def _to_out(settings: EmailNotificationSettings) -> EmailSettingsOut:
         from_email=settings.from_email,
         use_starttls=settings.use_starttls,
         use_ssl=settings.use_ssl,
-        alert_recipients=recipients,
+        warning_subject_template=settings.warning_subject_template,
+        alert_subject_template=settings.alert_subject_template,
+        warning_body_template=settings.warning_body_template,
+        alert_body_template=settings.alert_body_template,
         has_password=bool(settings.encrypted_smtp_password),
         updated_at=settings.updated_at,
     )
@@ -70,7 +72,10 @@ async def update_email_settings(
     settings.from_email = str(payload.from_email) if payload.from_email else None
     settings.use_starttls = payload.use_starttls
     settings.use_ssl = payload.use_ssl
-    settings.alert_recipients = [str(item) for item in payload.alert_recipients]
+    settings.warning_subject_template = payload.warning_subject_template.strip() if payload.warning_subject_template else None
+    settings.alert_subject_template = payload.alert_subject_template.strip() if payload.alert_subject_template else None
+    settings.warning_body_template = payload.warning_body_template.strip() if payload.warning_body_template else None
+    settings.alert_body_template = payload.alert_body_template.strip() if payload.alert_body_template else None
 
     if payload.clear_smtp_password:
         settings.encrypted_smtp_password = None

backend/app/models/models.py

@@ -134,7 +134,10 @@ class EmailNotificationSettings(Base):
     from_email: Mapped[str | None] = mapped_column(String(255), nullable=True)
     use_starttls: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
     use_ssl: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
-    alert_recipients: Mapped[list] = mapped_column(JSON, nullable=False, default=list)
+    warning_subject_template: Mapped[str | None] = mapped_column(Text, nullable=True)
+    alert_subject_template: Mapped[str | None] = mapped_column(Text, nullable=True)
+    warning_body_template: Mapped[str | None] = mapped_column(Text, nullable=True)
+    alert_body_template: Mapped[str | None] = mapped_column(Text, nullable=True)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),

backend/app/schemas/admin_settings.py

@@ -12,7 +12,10 @@ class EmailSettingsOut(BaseModel):
     from_email: EmailStr | None
     use_starttls: bool
     use_ssl: bool
-    alert_recipients: list[EmailStr]
+    warning_subject_template: str | None
+    alert_subject_template: str | None
+    warning_body_template: str | None
+    alert_body_template: str | None
     has_password: bool
     updated_at: datetime | None
 
@@ -28,7 +31,10 @@ class EmailSettingsUpdate(BaseModel):
     from_email: EmailStr | None = None
     use_starttls: bool = True
     use_ssl: bool = False
-    alert_recipients: list[EmailStr] = []
+    warning_subject_template: str | None = None
+    alert_subject_template: str | None = None
+    warning_body_template: str | None = None
+    alert_body_template: str | None = None
 
     @field_validator("smtp_port")
     @classmethod

backend/app/services/alert_notifications.py

@@ -81,6 +81,32 @@ def _render_body(item) -> str:
     return "\n".join(lines)
 
 
+def _template_context(item) -> dict[str, str]:
+    return {
+        "severity": str(item.severity),
+        "target_name": str(item.target_name),
+        "target_id": str(item.target_id),
+        "alert_name": str(item.name),
+        "category": str(item.category),
+        "description": str(item.description),
+        "message": str(item.message),
+        "value": "" if item.value is None else str(item.value),
+        "warning_threshold": "" if item.warning_threshold is None else str(item.warning_threshold),
+        "alert_threshold": "" if item.alert_threshold is None else str(item.alert_threshold),
+        "checked_at": item.checked_at.isoformat() if item.checked_at else "",
+        "alert_key": str(item.alert_key),
+    }
+
+
+def _safe_format(template: str | None, context: dict[str, str], fallback: str) -> str:
+    if not template:
+        return fallback
+    rendered = template
+    for key, value in context.items():
+        rendered = rendered.replace("{" + key + "}", value)
+    return rendered
+
+
 async def process_target_owner_notifications(db: AsyncSession, status: AlertStatusResponse) -> None:
     settings = await db.scalar(select(EmailNotificationSettings).limit(1))
     if not settings or not settings.enabled:
@@ -125,8 +151,15 @@ async def process_target_owner_notifications(db: AsyncSession, status: AlertStat
         should_send = existing is None or (now - existing.last_sent_at) >= _NOTIFICATION_COOLDOWN
 
         if should_send:
-            subject = _render_subject(item)
-            body = _render_body(item)
+            fallback_subject = _render_subject(item)
+            fallback_body = _render_body(item)
+            context = _template_context(item)
+            if item.severity == "alert":
+                subject = _safe_format(settings.alert_subject_template, context, fallback_subject)
+                body = _safe_format(settings.alert_body_template, context, fallback_body)
+            else:
+                subject = _safe_format(settings.warning_subject_template, context, fallback_subject)
+                body = _safe_format(settings.warning_body_template, context, fallback_body)
             for recipient in recipients:
                 try:
                     await _smtp_send(