diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 3ff7240b1..8fb418d2c 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -610,41 +610,11 @@ parameters:
 			count: 1
 			path: program/lib/Roundcube/cache/db.php
 
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 3
-			path: program/lib/Roundcube/cache/memcache.php
-
 		-
 			message: "#^Offset non\\-falsy\\-string does not exist on array\\{\\}\\.$#"
 			count: 1
 			path: program/lib/Roundcube/cache/memcache.php
 
-		-
-			message: "#^Static property rcube_cache_memcache\\:\\:\\$memcache \\(Memcache\\) does not accept false\\.$#"
-			count: 2
-			path: program/lib/Roundcube/cache/memcache.php
-
-		-
-			message: "#^Method rcube_cache_memcached\\:\\:engine\\(\\) should return Memcache but returns Memcached\\.$#"
-			count: 1
-			path: program/lib/Roundcube/cache/memcached.php
-
-		-
-			message: "#^Method rcube_cache_memcached\\:\\:engine\\(\\) should return Memcache but returns Memcached\\|false\\.$#"
-			count: 1
-			path: program/lib/Roundcube/cache/memcached.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 3
-			path: program/lib/Roundcube/cache/memcached.php
-
-		-
-			message: "#^Static property rcube_cache_memcached\\:\\:\\$memcache \\(Memcached\\) does not accept false\\.$#"
-			count: 2
-			path: program/lib/Roundcube/cache/memcached.php
-
 		-
 			message: "#^Call to function method_exists\\(\\) with Redis and 'del' will always evaluate to true\\.$#"
 			count: 1
@@ -760,11 +730,6 @@ parameters:
 			count: 1
 			path: program/lib/Roundcube/rcube.php
 
-		-
-			message: "#^Property rcube\\:\\:\\$memcached \\(Memcached\\|null\\) does not accept Memcache\\.$#"
-			count: 1
-			path: program/lib/Roundcube/rcube.php
-
 		-
 			message: "#^Property rcube\\:\\:\\$plugins \\(rcube_plugin_api\\) does not accept rcube_dummy_plugin_api\\.$#"
 			count: 1
@@ -1630,131 +1595,6 @@ parameters:
 			count: 1
 			path: program/lib/Roundcube/rcube_washtml.php
 
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_db\\:\\:save\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/db.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_db\\:\\:update\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/db.php
-
-		-
-			message: "#^Parameter \\#2 \\$newvars \\(string\\) of method rcube_session_db\\:\\:update\\(\\) should be contravariant with parameter \\$newvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/db.php
-
-		-
-			message: "#^Parameter \\#2 \\$vars \\(string\\) of method rcube_session_db\\:\\:save\\(\\) should be contravariant with parameter \\$vars \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/db.php
-
-		-
-			message: "#^Parameter \\#3 \\$oldvars \\(string\\) of method rcube_session_db\\:\\:update\\(\\) should be contravariant with parameter \\$oldvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/db.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_memcache\\:\\:save\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_memcache\\:\\:update\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Parameter \\#2 \\$newvars \\(string\\) of method rcube_session_memcache\\:\\:update\\(\\) should be contravariant with parameter \\$newvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Parameter \\#2 \\$vars \\(string\\) of method rcube_session_memcache\\:\\:save\\(\\) should be contravariant with parameter \\$vars \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Parameter \\#3 \\$oldvars \\(string\\) of method rcube_session_memcache\\:\\:update\\(\\) should be contravariant with parameter \\$oldvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcache.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_memcached\\:\\:save\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_memcached\\:\\:update\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Parameter \\#2 \\$newvars \\(string\\) of method rcube_session_memcached\\:\\:update\\(\\) should be contravariant with parameter \\$newvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Parameter \\#2 \\$vars \\(string\\) of method rcube_session_memcached\\:\\:save\\(\\) should be contravariant with parameter \\$vars \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Parameter \\#3 \\$oldvars \\(string\\) of method rcube_session_memcached\\:\\:update\\(\\) should be contravariant with parameter \\$oldvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/memcached.php
-
-		-
-			message: "#^Call to function method_exists\\(\\) with Redis and 'del' will always evaluate to true\\.$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_redis\\:\\:save\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Parameter \\#1 \\$key \\(string\\) of method rcube_session_redis\\:\\:update\\(\\) should be contravariant with parameter \\$key \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Parameter \\#2 \\$newvars \\(string\\) of method rcube_session_redis\\:\\:update\\(\\) should be contravariant with parameter \\$newvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Parameter \\#2 \\$vars \\(array\\) of method rcube_session_redis\\:\\:save\\(\\) should be contravariant with parameter \\$vars \\(mixed\\) of method rcube_session\\:\\:save\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Parameter \\#3 \\$oldvars \\(string\\) of method rcube_session_redis\\:\\:update\\(\\) should be contravariant with parameter \\$oldvars \\(mixed\\) of method rcube_session\\:\\:update\\(\\)$#"
-			count: 1
-			path: program/lib/Roundcube/session/redis.php
-
-		-
-			message: "#^Property rcube\\:\\:\\$storage \\(rcube_storage\\|null\\) does not accept StorageMock\\.$#"
-			count: 1
-			path: tests/ActionTestCase.php
-
 		-
 			message: "#^Parameter \\#1 \\$browser \\(Tests\\\\Browser\\\\Browser\\) of method Tests\\\\Browser\\\\Components\\\\App\\:\\:assert\\(\\) should be contravariant with parameter \\$browser \\(Laravel\\\\Dusk\\\\Browser\\) of method Laravel\\\\Dusk\\\\Component\\:\\:assert\\(\\)$#"
 			count: 1
diff --git a/program/lib/Roundcube/cache/memcache.php b/program/lib/Roundcube/cache/memcache.php
index 9f5165e03..26dfc7441 100644
--- a/program/lib/Roundcube/cache/memcache.php
+++ b/program/lib/Roundcube/cache/memcache.php
@@ -27,7 +27,7 @@ class rcube_cache_memcache extends rcube_cache
     /**
      * Instance of memcache handler
      *
-     * @var Memcache
+     * @var Memcache|false|null
      */
     protected static $memcache;
 
@@ -44,7 +44,7 @@ class rcube_cache_memcache extends rcube_cache
     /**
      * Get global handle for memcache access
      *
-     * @return Memcache
+     * @return Memcache|false
      */
     public static function engine()
     {
diff --git a/program/lib/Roundcube/cache/memcached.php b/program/lib/Roundcube/cache/memcached.php
index fa8df6dc3..8197744f8 100644
--- a/program/lib/Roundcube/cache/memcached.php
+++ b/program/lib/Roundcube/cache/memcached.php
@@ -27,7 +27,7 @@ class rcube_cache_memcached extends rcube_cache
     /**
      * Instance of memcached handler
      *
-     * @var Memcached
+     * @var Memcached|false|null
      */
     protected static $memcache;
 
@@ -50,7 +50,7 @@ class rcube_cache_memcached extends rcube_cache
     /**
      * Get global handle for memcache access
      *
-     * @return Memcache
+     * @return Memcached|false
      */
     public static function engine()
     {
diff --git a/program/lib/Roundcube/cache/redis.php b/program/lib/Roundcube/cache/redis.php
index 171e6ab0e..568d236d1 100644
--- a/program/lib/Roundcube/cache/redis.php
+++ b/program/lib/Roundcube/cache/redis.php
@@ -46,7 +46,7 @@ class rcube_cache_redis extends rcube_cache
     /**
      * Get global handle for redis access
      *
-     * @return Redis
+     * @return Redis|false
      */
     public static function engine()
     {
diff --git a/program/lib/Roundcube/rcube.php b/program/lib/Roundcube/rcube.php
index c51bfbefe..c883cf539 100644
--- a/program/lib/Roundcube/rcube.php
+++ b/program/lib/Roundcube/rcube.php
@@ -44,13 +44,13 @@ class rcube
     /** @var ?rcube_db Instance of database class */
     public $db;
 
-    /** @var ?Memcache Instance of Memcache class */
+    /** @var Memcache|false|null Instance of Memcache class */
     public $memcache;
 
-    /** @var ?Memcached Instance of Memcached class */
+    /** @var Memcached|false|null Instance of Memcached class */
     public $memcached;
 
-    /** @var ?Redis Instance of Redis class */
+    /** @var Redis|false|null Instance of Redis class */
     public $redis;
 
     /** @var ?rcube_session Instance of rcube_session class */
@@ -166,7 +166,7 @@ class rcube
     /**
      * Get global handle for memcache access
      *
-     * @return Memcache The memcache engine
+     * @return Memcache|false The memcache engine
      */
     public function get_memcache()
     {
@@ -180,7 +180,7 @@ class rcube
     /**
      * Get global handle for memcached access
      *
-     * @return Memcached The memcached engine
+     * @return Memcached|false The memcached engine
      */
     public function get_memcached()
     {
@@ -194,7 +194,7 @@ class rcube
     /**
      * Get global handle for redis access
      *
-     * @return Redis The redis engine
+     * @return Redis|false The redis engine
      */
     public function get_redis()
     {
diff --git a/program/lib/Roundcube/rcube_session.php b/program/lib/Roundcube/rcube_session.php
index 33760959c..2b798e064 100644
--- a/program/lib/Roundcube/rcube_session.php
+++ b/program/lib/Roundcube/rcube_session.php
@@ -142,8 +142,25 @@ abstract class rcube_session implements SessionHandlerInterface
     #[ReturnTypeWillChange]
     abstract public function read($key);
 
+    /**
+     * Write data to the session store
+     *
+     * @param string $key  Session identifier
+     * @param string $vars Session data
+     *
+     * @return bool True on success, False on failure
+     */
     abstract protected function save($key, $vars);
 
+    /**
+     * Write data to the session store
+     *
+     * @param string $key     Session identifier
+     * @param string $newvars New session data string
+     * @param string $oldvars Old session data string
+     *
+     * @return bool True on success, False on failure
+     */
     abstract protected function update($key, $newvars, $oldvars);
 
     /**
diff --git a/program/lib/Roundcube/session/memcache.php b/program/lib/Roundcube/session/memcache.php
index 176746092..a498c86f4 100644
--- a/program/lib/Roundcube/session/memcache.php
+++ b/program/lib/Roundcube/session/memcache.php
@@ -25,7 +25,7 @@
  */
 class rcube_session_memcache extends rcube_session
 {
-    /** @var Memcache The memcache driver */
+    /** @var Memcache|false|null The memcache driver */
     private $memcache;
 
     /** @var bool Debug state */
diff --git a/program/lib/Roundcube/session/memcached.php b/program/lib/Roundcube/session/memcached.php
index 6692f0181..a92dadf65 100644
--- a/program/lib/Roundcube/session/memcached.php
+++ b/program/lib/Roundcube/session/memcached.php
@@ -25,7 +25,7 @@
  */
 class rcube_session_memcached extends rcube_session
 {
-    /** @var Memcached The memcache driver */
+    /** @var Memcached|false|null The memcache driver */
     private $memcache;
 
     /** @var bool Debug state */
diff --git a/program/lib/Roundcube/session/php.php b/program/lib/Roundcube/session/php.php
index 8bdeedf88..134f0829e 100644
--- a/program/lib/Roundcube/session/php.php
+++ b/program/lib/Roundcube/session/php.php
@@ -49,9 +49,15 @@ class rcube_session_php extends rcube_session
         return '';
     }
 
-    protected function save($key, $vars) {}
+    protected function save($key, $vars)
+    {
+        return true;
+    }
 
-    protected function update($key, $newvars, $oldvars) {}
+    protected function update($key, $newvars, $oldvars)
+    {
+        return true;
+    }
 
     /**
      * Object constructor
diff --git a/program/lib/Roundcube/session/redis.php b/program/lib/Roundcube/session/redis.php
index e1f674542..acb103683 100644
--- a/program/lib/Roundcube/session/redis.php
+++ b/program/lib/Roundcube/session/redis.php
@@ -87,6 +87,7 @@ class rcube_session_redis extends rcube_session
     {
         if ($key) {
             try {
+                // @phpstan-ignore-next-line
                 $result = method_exists($this->redis, 'del')
                     ? $this->redis->del($key)
                     : $this->redis->delete($key);
@@ -171,7 +172,7 @@ class rcube_session_redis extends rcube_session
      * Write data to redis store
      *
      * @param string $key  Session identifier
-     * @param array  $vars Session data
+     * @param string $vars Session data
      *
      * @return bool True on success, False on failure
      */
diff --git a/tests/ActionTestCase.php b/tests/ActionTestCase.php
index 7978ad79d..17222bb13 100644
--- a/tests/ActionTestCase.php
+++ b/tests/ActionTestCase.php
@@ -146,7 +146,7 @@ class ActionTestCase extends TestCase
     public static function mockStorage()
     {
         $rcmail = rcmail::get_instance();
-        $rcmail->storage = new StorageMock();
+        $rcmail->storage = new StorageMock(); // @phpstan-ignore-line
 
         return $rcmail->storage;
     }