diff --git a/og_mailinglist_api.inc b/og_mailinglist_api.inc
index d8d95a52361cb0554d9eefe3d26fa6e9a92398d8..b249cd2fbeed34f44a95e8a77826d067dcca5a5c 100644
--- a/og_mailinglist_api.inc
+++ b/og_mailinglist_api.inc
@@ -207,10 +207,27 @@ function og_mailinglist_delete_thread_subscription($nid, $uid) {
   return $result;
 }
 
-/*
- * Log successful sent email.
+/**
+ * Log when email has been successfully sent.
+ *
+ * @param string $source
+ *   Indicates where the email came from, could be 'web' or 'email'.
+ * @param int $nid
+ *   Node ID.
+ * @param int $cid
+ *   Comment ID.
+ * @param string $parent_message_id
+ *   Parent email's message ID, could be something like <123.431@example.org>
+ * @param array $headers
+ *   Email headers as used in e.g _og_mailinglist_email_node_email()
+ * @return boolean
+ *   Indicates whether the logging was successful.
  */
-function og_mailinglist_log_email_sent($source, $nid, $cid = 0, $message_id = 0, $in_reply_to = 0, $references = 0, $parent_message_id = 0) {
+function og_mailinglist_log_email_sent($source, $nid, $cid = 0, $parent_message_id = 0, $headers = array()) {
+  $message_id = isset($headers['message-id']) ? $headers['message-id'] : 0;
+  $in_reply_to = isset($headers['in-reply-to']) ? $headers['in-reply-to'] : 0;
+  $references = isset($headers['references']) ? $headers['references'] : 0;
+
   $data = array(
     'nid' => $nid,
     'cid' => $cid,
@@ -292,7 +309,16 @@ function _og_mailinglist_get_thread_parent_messageid(&$headers) {
   }
 }
 
-function _og_mailinglist_get_nid_from_parent_messageid($message_id) {
+/**
+ * Get the node ID from the email's message ID.
+ *
+ * @param string $message_id
+ *   Email message ID, something like <13251.1353@example.com> or
+ *   <node-1-comment-3@example.org>
+ * @return int
+ *   Node nid of the thread.
+ */
+function _og_mailinglist_get_nid_from_messageid($message_id) {
   return db_query("SELECT nid
     FROM {og_mailinglist_source}
     WHERE message_id = :message_id",
diff --git a/og_mailinglist_phpmailer.inc b/og_mailinglist_phpmailer.inc
index fe9db1c035b41532b794548428ae99618eeb662d..818de960aaa5d382c722f667d29ee19239d41f98 100644
--- a/og_mailinglist_phpmailer.inc
+++ b/og_mailinglist_phpmailer.inc
@@ -186,7 +186,7 @@ function og_mailinglist_send_node_email($node, $gids) {
   }
 
   if ($success) {
-    og_mailinglist_log_email_sent('web', $node->nid, 0, $headers['message-id'], 0, 0, $headers['message-id']);
+    og_mailinglist_log_email_sent('web', $node->nid, 0, $headers['message-id'], $headers);
   }
   else {
     watchdog('og_mailinglist', "OG_Mailinglist couldn't send a new node email for node.", NULL, WATCHDOG_ERROR);
diff --git a/og_mailinglist_transport.inc b/og_mailinglist_transport.inc
index 2fb21c61b700b4d1dab5703879d6961020b1307a..04646813f0213be09c7037daf04abb1b2596af4c 100644
--- a/og_mailinglist_transport.inc
+++ b/og_mailinglist_transport.inc
@@ -407,7 +407,7 @@ function og_mailinglist_save_comment(&$email, $group_nodes, $node) {
   // Log that this comment came by email.
   $in_reply_to = isset($email['headers']['in-reply-to']) ? $email['headers']['in-reply-to'] : '';
   $references = isset($email['headers']['references']) ? $email['headers']['references'] : '';
-  og_mailinglist_log_email_sent('email', $node->nid, $comment->cid, $email['headers']['message-id'], $in_reply_to, $references, $parent_message_id);
+  og_mailinglist_log_email_sent('email', $node->nid, $comment->cid, $parent_message_id, $email['headers']);
 
   // Report activity to watchdog.
   $group_list = array();
@@ -473,7 +473,7 @@ function og_mailinglist_save_node(&$email, $group_nodes) {
   _og_mailinglist_email_node_email($email, $node, $group_nodes);
 
   // Log that this node came from email.
-  og_mailinglist_log_email_sent('email', $node->nid, 0, $email['headers']['message-id'], 0, 0, $email['headers']['message-id']);
+  og_mailinglist_log_email_sent('email', $node->nid, 0, $email['headers']['message-id'], $email['headers']);
 
   $group_list = array();
   foreach ($group_nodes as $gid => $group_node) {
@@ -1026,7 +1026,7 @@ function og_mailinglist_parse_nid($email) {
   // Check the in-reply-to header.
   $parent_message_id = _og_mailinglist_get_thread_parent_messageid($email['headers']);
   if (!empty($parent_message_id)) {
-    $nid = _og_mailinglist_get_nid_from_parent_messageid($parent_message_id);
+    $nid = _og_mailinglist_get_nid_from_messageid($parent_message_id);
   }
 
   if ($nid) {