Fix email From configuration

config/notifiers.go

@@ -118,7 +118,6 @@ func (c *EmailConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if c.To == "" {
 		return fmt.Errorf("missing to address in email config")
 	}
-
 	// Header names are case-insensitive, check for collisions.
 	normalizedHeaders := map[string]string{}
 	for h, v := range c.Headers {
@@ -129,15 +128,6 @@ func (c *EmailConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		normalizedHeaders[normalized] = v
 	}
 	c.Headers = normalizedHeaders
-	if _, ok := c.Headers["Subject"]; !ok {
-		c.Headers["Subject"] = DefaultEmailSubject
-	}
-	if _, ok := c.Headers["To"]; !ok {
-		c.Headers["To"] = c.To
-	}
-	if _, ok := c.Headers["From"]; !ok {
-		c.Headers["From"] = c.From
-	}
 
 	return checkOverflow(c.XXX, "email config")
 }

notify/impl.go

@@ -128,6 +128,15 @@ type Email struct {
 
 // NewEmail returns a new Email notifier.
 func NewEmail(c *config.EmailConfig, t *template.Template) *Email {
+	if _, ok := c.Headers["Subject"]; !ok {
+		c.Headers["Subject"] = config.DefaultEmailSubject
+	}
+	if _, ok := c.Headers["To"]; !ok {
+		c.Headers["To"] = c.To
+	}
+	if _, ok := c.Headers["From"]; !ok {
+		c.Headers["From"] = c.From
+	}
 	return &Email{conf: c, tmpl: t}
 }
 
@@ -229,8 +238,8 @@ func (n *Email) Notify(ctx context.Context, as ...*types.Alert) error {
 	}
 	defer wc.Close()
 
-	for header, name := range n.conf.Headers {
-		value, err := n.tmpl.ExecuteTextString(name, data)
+	for header, t := range n.conf.Headers {
+		value, err := n.tmpl.ExecuteTextString(t, data)
 		if err != nil {
 			return fmt.Errorf("executing %q header template: %s", header, err)
 		}