diff --git a/src/Module/Photo.php b/src/Module/Photo.php
index d1b4b9629e..c521d2be82 100644
--- a/src/Module/Photo.php
+++ b/src/Module/Photo.php
@@ -352,11 +352,11 @@ class Photo extends BaseModule
 				}
 				if (empty($mimetext)) {
 					if ($customsize <= Proxy::PIXEL_MICRO) {
-						$url = Contact::getDefaultAvatar($contact, Proxy::SIZE_MICRO);
+						$url = Contact::getDefaultAvatar($contact ?: [], Proxy::SIZE_MICRO);
 					} elseif ($customsize <= Proxy::PIXEL_THUMB) {
-						$url = Contact::getDefaultAvatar($contact, Proxy::SIZE_THUMB);
+						$url = Contact::getDefaultAvatar($contact ?: [], Proxy::SIZE_THUMB);
 					} else {
-						$url = Contact::getDefaultAvatar($contact, Proxy::SIZE_SMALL);
+						$url = Contact::getDefaultAvatar($contact ?: [], Proxy::SIZE_SMALL);
 					}
 				}
 				return MPhoto::createPhotoForExternalResource($url, 0, $mimetext);
diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index bfff5f84bb..60dd42cb49 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -303,7 +303,7 @@ class Processor
 		if (empty($activity['directmessage']) && ($activity['id'] != $activity['reply-to-id']) && !Post::exists(['uri' => $activity['reply-to-id']])) {
 			$recursion_depth = $activity['recursion-depth'] ?? 0;
 			Logger::notice('Parent not found. Try to refetch it.', ['parent' => $activity['reply-to-id'], 'recursion-depth' => $recursion_depth]);
-			if ($recursion_depth < 10) {
+			if ($recursion_depth < DI::config()->get('system', 'max_recursion_depth')) {
 				$result = self::fetchMissingActivity($activity['reply-to-id'], $activity, '', Receiver::COMPLETION_AUTO);
 				if (empty($result) && self::isActivityGone($activity['reply-to-id'])) {
 					// Recursively delete this and all depending entries
@@ -1207,13 +1207,19 @@ class Processor
 		$object = DI::cache()->get($cachekey);
 
 		if (!is_null($object)) {
-			Logger::debug('Fetch from cache', ['url' => $url, 'uid' => $uid]);
+			if (!empty($object)) {
+				Logger::debug('Fetch from cache', ['url' => $url, 'uid' => $uid]);
+			} else {
+				Logger::debug('Fetch from negative cache', ['url' => $url, 'uid' => $uid]);
+			}
 			return $object;
 		}
 
 		$object = ActivityPub::fetchContent($url, $uid);
 		if (empty($object)) {
 			Logger::notice('Activity was not fetchable, aborting.', ['url' => $url, 'uid' => $uid]);
+			// We perform negative caching.
+			DI::cache()->set($cachekey, [], Duration::FIVE_MINUTES);
 			return [];
 		}
 
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index f09541b13d..600fe31524 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -592,7 +592,7 @@ class Receiver
 			return;
 		}
 
-		if (!empty($object_data['entry-id']) && ($push || ($activity['completion-mode'] == self::COMPLETION_RELAY))) {
+		if (!empty($object_data['entry-id']) && DI::config()->get('system', 'decoupled_receiver') && ($push || ($activity['completion-mode'] == self::COMPLETION_RELAY))) {
 			// We delay by 5 seconds to allow to accumulate all receivers
 			$delayed = date(DateTimeFormat::MYSQL, time() + 5);
 			Logger::debug('Initiate processing', ['id' => $object_data['entry-id'], 'uri' => $object_data['object_id']]);
diff --git a/src/Protocol/Diaspora.php b/src/Protocol/Diaspora.php
index 62c8ce71c4..5c0f9b8131 100644
--- a/src/Protocol/Diaspora.php
+++ b/src/Protocol/Diaspora.php
@@ -3114,7 +3114,7 @@ class Diaspora
 			Logger::notice('Empty addr', ['contact' => $contact ?? [], 'callstack' => System::callstack(20)]);
 		}
 
-		$envelope = self::buildMessage($msg, $owner, $contact, $owner['uprvkey'], $pubkey, $public_batch);
+		$envelope = self::buildMessage($msg, $owner, $contact, $owner['uprvkey'], $pubkey ?? '', $public_batch);
 
 		$return_code = self::transmit($owner, $contact, $envelope, $public_batch, $guid);
 
diff --git a/static/defaults.config.php b/static/defaults.config.php
index 1876ea90d7..a8a23ea9e9 100644
--- a/static/defaults.config.php
+++ b/static/defaults.config.php
@@ -164,6 +164,10 @@ return [
 		// Whether to use Memcache, Memcached, Redis or APCu to store temporary cache.
 		'cache_driver' => 'database',
 
+		// decoupled_receiver (Boolean)
+		// Decouple incoming AP posts by doing the processing in the background.
+		'decoupled_receiver' => true,
+
 		// distributed_cache_driver (database|memcache|memcached|redis)
 		// Whether to use database, Memcache, Memcached or Redis as a distributed cache.
 		'distributed_cache_driver' => 'database',
@@ -416,6 +420,10 @@ return [
 		// Maximum number of concurrent database processes for foreground tasks.
 		'max_processes_frontend' => 20,
 
+		// max_recursion_depth (Integer)
+		// Maximum recursion depth when fetching posts until the job is delegated to a worker task.
+		'max_recursion_depth' => 10,
+
 		// maximagesize (Integer)
 		// Maximum size in bytes of an uploaded photo.
 		'maximagesize' => 800000,