Resolution:
The size of the message put on the wire is less than the one maintained in memory.  When you hold on to data in memory, ie.
creating the messages and keeping it in memory before sending, it  will consume more memory than the actual payload in the wire.

For example, if you are holding 10,000 messages each with 300 bytes of data then you can expect that the total memory allocated could be around 9,000,000 (overhead per message in memory is roughly around 600 bytes).