From 3c4a2651e7a642bc0f2305ec5ead4e4aa3a0f4c5 Mon Sep 17 00:00:00 2001
From: gutmet <me.git@gutmet.org>
Date: Sat, 21 Nov 2020 10:25:27 +0100
Subject: [PATCH] set sender and reply-to only if dkim does not prevent it

---
 picolist.go | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/picolist.go b/picolist.go
index 40caf0b..bd487c1 100644
--- a/picolist.go
+++ b/picolist.go
@@ -102,15 +102,25 @@ func isAllowed(mail *mail.Message, f flags, owners hashset) (bool, error) {
 }
 
 func setHeaderFields(mail *mail.Message, listname string, f flags) {
+	dkim := mail.Header.Get("DKIM-Signature")
+	canChange := func(headerName string) bool {
+		headerName = ":" + headerName + ":"
+		headerNameLower := strings.ToLower(headerName)
+		return dkim == "" || (!strings.Contains(dkim, headerName) && !strings.Contains(dkim, headerNameLower))
+	}
 	bounceAddress := []string{"<" + f.returnPath() + ">"}
 	listAddress := []string{"<" + listname + ">"}
 	mail.Header["Precedence"] = []string{"list"}
-	mail.Header["Sender"] = bounceAddress
+	if canChange("Sender") {
+		mail.Header["Sender"] = bounceAddress
+	}
 	mail.Header["Errors-To"] = bounceAddress
 	mail.Header["List-Id"] = listAddress
 	if !f.newsletter {
 		mail.Header["List-Post"] = []string{"<mailto:" + listname + ">"}
-		mail.Header["Reply-To"] = listAddress
+		if canChange("Reply-To") {
+			mail.Header["Reply-To"] = listAddress
+		}
 	}
 }