mail log reporting error every minute
 

i am new to linux and have set up a server. I am getting an error in my mail log:

Oct 25 20:05:11 japan postfix/cleanup[3603]: fatal: unsupported dictionary type: mysql
Oct 25 20:05:12 japan postfix/master[2307]: warning: process /usr/libexec/postfix/cleanup pid 3603 exit status 1
Oct 25 20:05:12 japan postfix/master[2307]: warning: /usr/libexec/postfix/cleanup: bad command startup -- throttling

have searched google and can't make heads or tails of it.
this happens every minute or so.
any1 got any ideas?

also what is this cleanup thing?