MailScanner issue with postfix

[Angela Schwalm]

hi,

displaying all running processes with "top" I've noticed sth. strange:

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
   :
  509 postfix   20   0  8020  524   424 S     0.0  0.8   0:00 MailScanner
  510 postfix   20   0 16288 2500   912 S     0.0  4.0   0:07 MailScanner
  521 postfix   20   0 15664  640   248 S     0.0  1.0   0:07 MailScanner
  522 postfix   20   0     0    0     0 Z     0.0  0.0   0:00 MailScanner
<defunct>
  524 postfix    1   0     0    0     0 Z     0.0  0.0   0:00 MailScanner
<defunct>
  525 postfix   20   0 16640 7908  1820 S     0.0 12.7   0:07 MailScanner
  526 postfix    1   0     0    0     0 Z     0.0  0.0   0:00 MailScanner
<defunct>
  527 postfix   20   0 16788  14M  3872 S     0.0 23.2   0:07 MailScanner
  528 postfix   20   0 16784  14M  3880 S     0.0 23.2   0:07 MailScanner
  530 postfix    8   0     0    0     0 Z     0.0  0.0   0:00 MailScanner
<defunct>
  532 postfix    0   0     0    0     0 Z     0.0  0.0   0:00 MailScanner
<defunct>

Could anybody explain that?