Use Mail-Followup-To header to determine recipients according to
http://cr.yp.to/proto/replyto.html if configured and present in the
message being replied to.
---
 notmuch-reply.c |   25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/notmuch-reply.c b/notmuch-reply.c
index 22c58ff..604691a 100644
--- a/notmuch-reply.c
+++ b/notmuch-reply.c
@@ -324,6 +324,7 @@ add_recipients_from_message (GMimeMessage *reply,
 	{ "bcc",        NULL, GMIME_RECIPIENT_TYPE_BCC }
     };
     const char *from_addr = NULL;
+    const char *recipients;
     unsigned int i;
     unsigned int n = 0;
 
@@ -343,9 +344,29 @@ add_recipients_from_message (GMimeMessage *reply,
 	reply_to_map[0].fallback = NULL;
     }
 
-    for (i = 0; i < ARRAY_SIZE (reply_to_map); i++) {
-	const char *recipients;
+    /* Use Mail-Followup-To header to determine recipients according
+     * to http://cr.yp.to/proto/replyto.html if configured and present
+     * in the message being replied to.
+     */
+    if (reply_all && notmuch_config_get_reply_honor_followup_to (config)) {
+	recipients = notmuch_message_get_header (message, "mail-followup-to");
+	if (recipients && *recipients) {
+	    n = scan_address_string (recipients, config, reply,
+				     GMIME_RECIPIENT_TYPE_TO, &from_addr);
+	    if (n) {
+		/* Same rationale as in the loop below. */
+		reply = NULL;
+
+		/* From address and some recipients are enough, bail out. */
+		if (from_addr)
+		    return from_addr;
+
+		/* Else need to find from address in other headers. */
+	    }
+	}
+    }
 
+    for (i = 0; i < ARRAY_SIZE (reply_to_map); i++) {
 	recipients = notmuch_message_get_header (message,
 						 reply_to_map[i].header);
 	if ((recipients == NULL || recipients[0] == '\0') && reply_to_map[i].fallback)
-- 
1.7.10.4