Add header to suppress OOO auto-replies (fixes #86)

Author: fmarier

services/ses.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	htmlTemplate "html/template"
+	"maps"
 	"os"
 	"strconv"
 	textTemplate "text/template"
@@ -38,6 +39,10 @@ const (
 	expiresHeaderName  = "X-Expires-At"
 )
 
+var defaultEmailHeaders = map[string]string{
+	"X-Auto-Response-Suppress": "All", // Suppress out-of-office auto-replies
+}
+
 type SESService struct {
 	client              *sesv2.Client
 	verifyHTMLTemplate  *htmlTemplate.Template
@@ -198,9 +203,11 @@ func (s *SESService) sendEmail(ctx context.Context, email string, subject string
 		},
 	}
 
-	if len(headers) > 0 {
-		message.Headers = make([]types.MessageHeader, 0, len(headers))
-		for name, value := range headers {
+	mergedHeaders := maps.Clone(defaultEmailHeaders)
+	maps.Copy(mergedHeaders, headers)
+	if len(mergedHeaders) > 0 {
+		message.Headers = make([]types.MessageHeader, 0, len(mergedHeaders))
+		for name, value := range mergedHeaders {
 			message.Headers = append(message.Headers, types.MessageHeader{
 				Name:  &name,
 				Value: &value,