[exim] 500 Firewall Error

Hey all,

I somtimes get the following error when I deliver mail to some sites,
The deliveries are most of the time successful for the same hosts but
sometimes get the error. Tried to look and do the tests but everything
works well when I do them by hand. I even added
"DELIVER_OUT_BUFFER_SIZE=512" in the config file but does not really
help.

2006-11-16 12:24:25 1GkdAP-000Amj-HA ** nobody@???
F=<somebody@???> P=<nobody@???> R=dnslookup T=remote_smtp:
SMTP error from remote mail server after MAIL FROM:<nobody@???>
SIZE=11462: host mailmarshal5.standardbank.co.za [196.8.126.8]: 500
Firewall Error

Thanks