as reported by Rafal Nowak, $protocolVersion should always be a string, since floats when converted to strings will use the decimal separator defined by current locale. spamd will always expect a dot.

Author: Pedro Padron

SpamAssassin/Client.php

@@ -26,7 +26,7 @@ class SpamAssassin_Client
 
     protected $socketPath;
     protected $socket;
-    protected $protocolVersion = 1.5;
+    protected $protocolVersion = '1.5';
     protected $enableZlib;
 
     /**
@@ -429,4 +429,4 @@ public function revoke($message)
         return $this->exec('TELL', $message, $additionalHeaders)->didSet;
     }
 
-}
+}