Fix #590.

diff --git a/send.c b/send.c
index ba96997fc4130315fd155269064c70e9ac213b3a..e30a39a4ffd28c91261302153cf8613ca57ed61e 100644 (file)
--- a/send.c
+++ b/send.c
@@ -630,8 +630,11 @@ mutt_make_reference_headers (ENVELOPE *curenv, ENVELOPE *env, CONTEXT *ctx)
   else
   {
     env->references = mutt_make_references (curenv);
-    env->in_reply_to = mutt_new_list ();
-    env->in_reply_to->data = safe_strdup (curenv->message_id);
+    if (curenv->message_id)
+    {
+      env->in_reply_to = mutt_new_list ();
+      env->in_reply_to->data = safe_strdup (curenv->message_id);
+    }
   }
 }