I am not sure but wasn't there an option to immediately react to an enemy blockading your outpost? They always blockade my early outposts and I can't say a thing.

They go on the list, I rember well those that block me at the start. Their home planet is a small price to pay for their insulance. 

You'll often get diplomatic options to make the offender move or suffer a penalty; of course you could always just send a fleet to drive off the blockading ship.  It's one of those things you have to anticipate and be prepared to answer when it happens.

Yeah there is an option for when smb is within your influence area, but there is no influence area for the outpost and this proposal seems to be unavailable.

 It's one of those things you have to anticipate and be prepared to answer when it happens.

I don't think it is productive to build fleets that early (before turn 10 basically), when you haven't even finished your industry buildings and data ship yards. And I recently switched from keeping some weapons on my hero ship and scouts to going full probes and saving some extra money (due to the recent removal of probe exploit). And very often their blockades just get destroyed by pirates - another point why I don't want to blockade myself. My concern is more about just having an option to raise diplomatic pressure for that hostile action and getting a feel of whats coming next based on the response.