diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index d6140535b9..78a7f37b8c 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -1111,6 +1111,10 @@ class Processor
 			}
 
 			if (!empty($activity['directmessage']) && self::postMail($item)) {
+				if (!empty($item['source']) && DI::config()->get('debug', 'store_source')) {
+					Post\Activity::insert($item['uri-id'], $item['source']);
+				}
+		
 				continue;
 			}
 
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index f195c8b9e6..e6371a5975 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -436,15 +436,11 @@ class Receiver
 
 			$object_data['object_id'] = $object_id;
 
-			// Test if it is an answer to a mail
-			if (DBA::exists('mail', ['uri' => $object_data['reply-to-id']])) {
+			// Test if it is a direct message
+			if (self::checkForDirectMessage($object_data, $activity)) {
 				$object_data['directmessage'] = true;
-			} else {
-				$object_data['directmessage'] = JsonLD::fetchElement($activity, 'litepub:directMessage');
-
-				if (!empty(JsonLD::fetchElement($activity['as:object'], 'misskey:_misskey_talk'))) {
-					$object_data = self::setChatData($object_data, $receivers);
-				}
+			} elseif (!empty(JsonLD::fetchElement($activity['as:object'], 'misskey:_misskey_talk'))) {
+				$object_data = self::setChatData($object_data, $receivers);
 			}
 		} elseif (in_array($type, array_merge(self::ACTIVITY_TYPES, ['as:Announce', 'as:Follow'])) && in_array($object_type, self::CONTENT_TYPES)) {
 			// Create a mostly empty array out of the activity data (instead of the object).
@@ -523,6 +519,57 @@ class Receiver
 		return $object_data;
 	}
 
+	/**
+	 * Check if the received message is a direct message
+	 *
+	 * @param array $object_data
+	 * @param array $activity
+	 * @return boolean
+	 */
+	private static function checkForDirectMessage(array $object_data, array $activity): bool
+	{
+		if (DBA::exists('mail', ['uri' => $object_data['reply-to-id']])) {
+			return true;
+		}
+
+		if ($object_data['id'] != $object_data['reply-to-id']) {
+			return false;
+		}
+
+		if (JsonLD::fetchElement($activity, 'litepub:directMessage')) {
+			return true;
+		}
+
+		if (!empty($object_data['attachments'])) {
+			return false;
+		}
+
+		if (!empty($object_data['receiver_urls']['as:cc']) || empty($object_data['receiver_urls']['as:to'])) {
+			return false;
+		}
+
+		if ((count($object_data['receiver_urls']['as:to']) != 1) || !User::getIdForURL($object_data['receiver_urls']['as:to'][0])) {
+			return false;
+		}
+
+		$mentions = 0;
+		foreach ($object_data['tags'] as $mention) {
+			if ($mention['type'] != 'Mention') {
+				continue;
+			}
+			if (!User::getIdForURL($mention['href'])) {
+				return false;
+			}
+			++$mentions;
+		}
+
+		if ($mentions > 1) {
+			return false;
+		}
+
+		return true;
+	}
+
 	private static function setChatData(array $object_data, array $receivers): array
 	{
 		if (count($receivers) != 1) {