What's the best way to send large generic List to one client once.

What would be the best way to send a big List of 500 - 2.000.000 elements (Should be max. ~3.8MB) on Player Connect? I need to only send this once, because it’s for world synchronisation.

SyncVar won’t work for obvious reasons.

I’m not the holder of all knowledge to tell you “this is the best way”, but i would put the hole list as a JSON string send the string and read it on the client back to a List.

You can use JSONUtility, makes the work quite simple, just a single method call.