[Mimedefang] right value for MX_MAXIMUM

[Muthu N.C]

Hello,

I am having the system with sendmail, mimedefang and spamassassin.
Mimedefang is running with the below options.

-m 2 -x 80 -y 0 -U defang -b 300 -l

MX_MINIMUM=2
MX_MAXIMUM=80
#MX_QUEUE_SIZE=10

In a day I am getting the below error multiple times. By looking at
the md-mx-ctrl rawstats, all the 80 slaves are busy at that time. We
are receiving around 500 e-mails in a minute.

mimedefang-multiplexor[2500]: No free slaves
mimedefang[2517]: t5O6odRs007105: Error from multiplexor: error: No free slaves

How much slaves should be set for this workload?
Would increasing the MX_QUEUE_SIZE help, how much I can increase?
Any other suggestions to overcome this issue?
I read that the e-mails sent during this time would be retried by the
other MTA automatically, but I am seeing it as lost.

Thanks,
Muthu.