The Maximum message length on the system was wrongly configured on the MSS. If the MAS sends a message of 5 minutes to the MSS and the Maximum message length on the MSS is only configured for 2 minutes, it rejects the message, and the message stays on the MAS spool folder.
Problem Fix/Workaround/Solution
Need to increase the maximum message length size on the MSS.
Resolution Plan
1. Log into the MSS with Craft credentials.
2. Open the Messaging Attributes.
3. Set the Maximum Message Length to at least 15 minutes.
4. Save the configuration.
5. Once you restart the MAS service, you can see events 1461, indicating messaging are getting delivered from the Spool folder to the MSS
Ken Means
"I find that the harder I work, the more luck I seem to have."
- Thomas Jefferson (1743-1826)