MyBB Community Forums

After disabling the plugins in init.php by defining define("NO_PLUGINS", 1); this unknkown sender problem is solved.
But when I disabled the plugins in ACP one by one this problem did not go away.
My Mybb version is : 1.6.3
I've the following plugins installed:

• Registration Checkboxes Plugin(1.2)
  
• Akismet(1.2.1)
  
• Extra Forum Permissions(1.1)
  
• Google SEO(1.1.13)
  
• No Links Allowed(.1)
  
• Page Manager(1.5.2)
  
• Registration Security Question(1.)
  

Well I don't think those plugins can cause this problem.