[Mimedefang] urgent help need for " 451 4.7.1 Please try again later"

[Xiaoyan Ma]

We brought up mimedefang2.31 yesterday with sendmail 8-12.9 on solaris 8.

It worked fine yesterday, Sunday.  But today when the load is high, I got 
error message in the log:
451 4.7.1 Please try again later and user got the follow warning from their 
client:

There has been as error transferring your mail.  I said:  MAIL 
FROM:<XXX at xxxxxx> and then the SMTP server (haas.berkeley.edu) said  451 
4.7.1 Please try again later."


this is my mimedefang.conf file:
MX_MINIMUM=4

MX_MAXIMUM=20

MX_MAX_RSS=10000

MX_MAX_AS=30000

MX_IDLE=60

MX_BUSY=120


Any suggestions on how to adjust these numbers?

Thansk.

Xiaoyan