[Mailmunge] Temp fail due to unable to start worker.

[postfix at ptld.com]

I had an incoming email temp fail and the logs said

   mailmunge-mx[25275]: Starting worker 2 (pid 87320) (3 running): About 
to perform scan
   ...
   mailmunge-mx[25275]: Did not start worker 3: Not enough time elapsed 
since last worker activation
   mailmunge-mx[25275]: Unable to activate worker 3
   mailmunge[25284]: 4Gk5ZP2x4kz4l3jL: Error from multiplexor: error: 
Unable to activate worker
   postfix/cleanup[87315]: 4Gk5ZP2x4kz4l3jL: milter-reject: 
END-OF-MESSAGE from m107.em.secureserver.net[198.71.244.6]: 4.7.1 
Service unavailable - try again later; ...

My config has

   MX_MINIMUM=2
   MX_MAXIMUM=10
   MX_BUSY=30
   MX_IDLE=300
   MX_WORKER_DELAY=5
   MX_MIN_WORKER_DELAY=1
   MX_REQUESTS=500
   ALLOW_CONNECTIONS_TO_QUEUE=yes
   MX_QUEUE_SIZE=10
   MX_QUEUE_TIMEOUT=30

Where did i short change myself? Is it the MX_MIN_WORKER_DELAY and if i 
set that to 0 will it spawn new workers as fast as needed during burst? 
This incident happened when postfix was handling 10 concurrent 
connections from the same client. Im also wondering if workers were busy 
why didn't the connection get queued instead of temp failed?