A couple things here. As long as your JNDI connection factory is not configured to use “Direct Transport for Non-Persistent Messages”:
then when you subscribe to your temporary topic, the broker will create a anonymous Topic Endpoint for you with your subscription added:
By default, Topic Endpoints will not block new messages if they are full when another one is received. You can see this in the Topic Endpoints advanced Settings:
But the broker will just silently discard messages if your Topic Endpoint is totally full. But for the TTL aspect to your question, again by default the Topic is configured to respect whatever TTL value the publisher is setting on each message, and to discard old messages:
If you have configured a queue within the Message VPN called #DEAD_MSG_QUEUE then the expired messages will go in there.
BTW, on nomenclature… when you say “from my JMS endpoint”, are you referring to a JMS publisher application?
Hope that helps.