Ship cannot accept shipment [ 6681.2 / 6660 Cargo Space Used ]

I was sending exotic matter, which has no weight in your cargo.
Explain to me how that works.

they're overlimit, they can't take anything, not even something that takes up 0 space

It doesn't matter. Try sending CTP, Debris, or any other thing that doesn't take space, and it will tell you the same thing. Problem is, they INITIALLY register with your cargo space before reverting back to nothing (try it on your mineral pulls with EM, you'll see that the total space it takes up is equivalent to everything including EM before you sell it) The reason for this is that if it DIDN'T register, you could theoretically gain infinite EM per mineral pull.

I suspect this is a latent "glitch" left over from the old days when Exotic Matter DID take cargo space.

Well actually, think about it Darth...if it didn't temporarily take up space, what's to stop you from getting 20 million exotic matter in one mineral pull? Since there's no upper limit (like the cargo does now) you could get infinite amounts, making it broken and useless.

Like for example, if you had 100 space left, and you get 990 minerals and 10 Exotic Matter. Otherwise you'd get 1000 minerals and whatever EM happens to come your way, in infinitely possible quantities.

The amount of EM you get on a draw is based on your rank, the same as all the other minerals.