Hello,
The count given in this property will hold that number of sync messages in memory and once the count gets more than the defined limit the synchrnous message remover job will delete the message (in FIFO manner).
BTW, a general recommendation is that the value of this property should not be very high.
From sap help -
This property defines
the maximum number of synchronous message headers that are kept in memory for
monitoring and duplicate detection purposes. The synchronous-message-remover job
checks how many messages are in final state and could be completely removed from
memory.
Then it removes the
oldest synchronous message headers until a maximum number of message headers are
left in memory, as configured by the messageCount property
Thanks
Amit Srivastava