how to close sendmail in syslog-ng?

[nifi]

i use cacti and haloe(syslog) in debian/ubuntu,there is a lot of log info like this:
ubuntu 2007-07-30 10:35:36 sm-msp-queue[11813]: l6R8e2iF021623: to=postmaster, delay=2+17:40:05, xdelay=00:00:00, mailer=relay, pri=17064271, relay=[127.0.0.1] [127.0.0.1], dsn=4.0.0, stat=Deferred: Connection refused by [127.0.0.1]

I do not need mail alert,so how to close the mail in syslog-ng???