Add blackmail.HeadersAutoreply() to most emails

I'm getting some "Thanks for your inquiry" backscatter.

cron/email_reports.go

@@ -64,6 +64,7 @@ func emailReports(ctx context.Context) error {
 		err = blackmail.Send(subject,
 			blackmail.From("GoatCounter reports", goatcounter.Config(ctx).EmailFrom),
 			blackmail.To(user.Email),
+			blackmail.HeadersAutoreply(),
 			blackmail.BodyText(text),
 			blackmail.BodyHTML(html))
 		if err != nil {

export.go

@@ -203,6 +203,7 @@ func (e *Export) Run(ctx context.Context, fp *os.File, mailUser bool) {
 		err = blackmail.Send("GoatCounter export ready",
 			blackmail.From("GoatCounter export", Config(ctx).EmailFrom),
 			blackmail.To(user.Email),
+			blackmail.HeadersAutoreply(),
 			blackmail.BodyMustText(TplEmailExportDone{ctx, *site, *user, *e}.Render))
 		if err != nil {
 			l.Error(err)

handlers/settings.go

@@ -620,6 +620,7 @@ func (h settings) exportImport(w http.ResponseWriter, r *http.Request) error {
 			sendErr := blackmail.Send("GoatCounter import error",
 				blackmail.From("GoatCounter import", goatcounter.Config(r.Context()).EmailFrom),
 				blackmail.To(user.Email),
+				blackmail.HeadersAutoreply(),
 				blackmail.BodyMustText(goatcounter.TplEmailImportError{r.Context(), err}.Render))
 			if sendErr != nil {
 				zlog.Error(sendErr)

handlers/user.go

@@ -135,6 +135,7 @@ func (h user) requestReset(w http.ResponseWriter, r *http.Request) error {
 			T(ctx, "email/reset-user-email-subject|Password reset for %(domain)", site.Domain(ctx)),
 			blackmail.From("GoatCounter login", goatcounter.Config(ctx).EmailFrom),
 			blackmail.To(u.Email),
+			blackmail.HeadersAutoreply(),
 			blackmail.BodyMustText(goatcounter.TplEmailPasswordReset{ctx, *site, *u}.Render))
 		if err != nil {
 			zlog.Errorf("password reset: %s", err)