Messages Queued (Quotas Met)

Hi All,

We are facing huge number of delivery failure with error message "Messages Queued (Quotas Met)" on a specific domain continuously.

The current configuration of Mx rule set for the domain is given below:

Maximum number of Connection - 1

Maximum number of message - 3

Messages per hour - 50000

For a particular delivery on a single day, Out of 18486 we are facing 2042 messages failure with the same error "Messages Queued (Quotas Met)"    

What would be the best possible solution to eliminate this error and to ensure higher success rate of messages.