+/*
+ * Look for the user's address in " for <email@add.res>" in the
+ * received headers.
+ *
+ * Return the address that was found, if any, and NULL otherwise.
+ */
+static const char *
+guess_from_in_received_for (notmuch_config_t *config, const char *received)
+{
+ const char *ptr;
+
+ ptr = strstr (received, " for ");
+ if (! ptr)
+ return NULL;
+
+ return user_address_in_string (ptr, config);
+}
+
+/*
+ * Parse all the " by MTA ..." parts in received headers to guess the
+ * email address that this was originally delivered to.
+ *
+ * Extract just the MTA here by removing leading whitespace and
+ * assuming that the MTA name ends at the next whitespace. Test for
+ * *(by+4) to be non-'\0' to make sure there's something there at all
+ * - and then assume that the first whitespace delimited token that
+ * follows is the receiving system in this step of the receive chain.
+ *
+ * Return the address that was found, if any, and NULL otherwise.
+ */
+static const char *
+guess_from_in_received_by (notmuch_config_t *config, const char *received)
+{
+ const char *addr;
+ const char *by = received;
+ char *domain, *tld, *mta, *ptr, *token;
+
+ while ((by = strstr (by, " by ")) != NULL) {
+ by += 4;
+ if (*by == '\0')
+ break;
+ mta = xstrdup (by);
+ token = strtok(mta," \t");
+ if (token == NULL) {
+ free (mta);
+ break;
+ }
+ /*
+ * Now extract the last two components of the MTA host name as
+ * domain and tld.
+ */
+ domain = tld = NULL;
+ while ((ptr = strsep (&token, ". \t")) != NULL) {
+ if (*ptr == '\0')
+ continue;
+ domain = tld;
+ tld = ptr;
+ }
+
+ if (domain) {
+ /*
+ * Recombine domain and tld and look for it among the
+ * configured email addresses. This time we have a known
+ * domain name and nothing else - so the test is the other
+ * way around: we check if this is a substring of one of
+ * the email addresses.
+ */
+ *(tld - 1) = '.';
+
+ addr = string_in_user_address (domain, config);
+ if (addr) {
+ free (mta);
+ return addr;
+ }
+ }
+ free (mta);
+ }
+
+ return NULL;
+}
+
+/*
+ * Get the concatenated Received: headers and search from the front
+ * (last Received: header added) and try to extract from them
+ * indications to which email address this message was delivered.
+ *
+ * The Received: header is special in our get_header function and is
+ * always concatenated.
+ *
+ * Return the address that was found, if any, and NULL otherwise.
+ */
+static const char *
+guess_from_in_received_headers (notmuch_config_t *config,
+ notmuch_message_t *message)
+{
+ const char *received, *addr;
+ char *sanitized;
+
+ received = notmuch_message_get_header (message, "received");
+ if (! received)
+ return NULL;
+
+ sanitized = sanitize_string (NULL, received);
+ if (! sanitized)
+ return NULL;
+
+ addr = guess_from_in_received_for (config, sanitized);
+ if (! addr)
+ addr = guess_from_in_received_by (config, sanitized);
+
+ talloc_free (sanitized);
+
+ return addr;
+}
+
+/*
+ * Try to find user's email address in one of the extra To-like
+ * headers: Envelope-To, X-Original-To, and Delivered-To (searched in
+ * that order).
+ *
+ * Return the address that was found, if any, and NULL otherwise.
+ */
+static const char *
+get_from_in_to_headers (notmuch_config_t *config, notmuch_message_t *message)
+{
+ size_t i;
+ const char *tohdr, *addr;
+ const char *to_headers[] = {
+ "Envelope-to",
+ "X-Original-To",
+ "Delivered-To",
+ };
+
+ for (i = 0; i < ARRAY_SIZE (to_headers); i++) {
+ tohdr = notmuch_message_get_header (message, to_headers[i]);
+
+ /* Note: tohdr potentially contains a list of email addresses. */
+ addr = user_address_in_string (tohdr, config);
+ if (addr)
+ return addr;
+ }
+
+ return NULL;
+}
+
+static GMimeMessage *
+create_reply_message(void *ctx,
+ notmuch_config_t *config,
+ notmuch_message_t *message,
+ notmuch_bool_t reply_all)
+{
+ const char *subject, *from_addr = NULL;
+ const char *in_reply_to, *orig_references, *references;
+
+ /* The 1 means we want headers in a "pretty" order. */
+ GMimeMessage *reply = g_mime_message_new (1);
+ if (reply == NULL) {
+ fprintf (stderr, "Out of memory\n");
+ return NULL;
+ }
+
+ subject = notmuch_message_get_header (message, "subject");
+ if (subject) {
+ if (strncasecmp (subject, "Re:", 3))
+ subject = talloc_asprintf (ctx, "Re: %s", subject);
+ g_mime_message_set_subject (reply, subject);
+ }
+
+ from_addr = add_recipients_from_message (reply, config,
+ message, reply_all);
+
+ /*
+ * Sadly, there is no standard way to find out to which email
+ * address a mail was delivered - what is in the headers depends
+ * on the MTAs used along the way.
+ *
+ * If none of the user's email addresses are in the To: or Cc:
+ * headers, we try a number of heuristics which hopefully will
+ * answer this question.
+ *
+ * First, check for Envelope-To:, X-Original-To:, and
+ * Delivered-To: headers.
+ */
+ if (from_addr == NULL)
+ from_addr = get_from_in_to_headers (config, message);
+
+ /*
+ * Check for a (for <email@add.res>) clause in Received: headers,
+ * and the domain part of known email addresses in the 'by' part
+ * of Received: headers
+ */
+ if (from_addr == NULL)
+ from_addr = guess_from_in_received_headers (config, message);
+
+ /* Default to user's primary address. */
+ if (from_addr == NULL)
+ from_addr = notmuch_config_get_user_primary_email (config);
+
+ from_addr = talloc_asprintf (ctx, "%s <%s>",
+ notmuch_config_get_user_name (config),
+ from_addr);
+ g_mime_object_set_header (GMIME_OBJECT (reply),
+ "From", from_addr);
+
+ in_reply_to = talloc_asprintf (ctx, "<%s>",
+ notmuch_message_get_message_id (message));
+
+ g_mime_object_set_header (GMIME_OBJECT (reply),
+ "In-Reply-To", in_reply_to);
+
+ orig_references = notmuch_message_get_header (message, "references");
+ if (!orig_references)
+ /* Treat errors like missing References headers. */
+ orig_references = "";
+ references = talloc_asprintf (ctx, "%s%s%s",
+ *orig_references ? orig_references : "",
+ *orig_references ? " " : "",
+ in_reply_to);
+ g_mime_object_set_header (GMIME_OBJECT (reply),
+ "References", references);
+
+ return reply;
+}
+