[exim] load goes high

I am running about 20 servers with default exim configuration that cpanel
writes on the servers.



One of the servers get a very high load when some of the customers send
mails to

His clients through the VBulletin script.



These mails doesn't exceed 20 thousand mail , and when he sends load goes
very high,



However other servers sends maybe 40 thousand mails without a big problem ,
and with same configuration and specification.





What can I do , or where can I work around to decrease the exim consumption
of the load like that.



I' $ve tried queue_only_load=6 but no any benefit :-(



And thanks a lot