So the host that handed this mail to me was almost certainly not the originating site of the spam. Spammers don't generally play that way. When you have a valid Received line, it's generally safe to assume that the previous Received line was filled in by an honest host. This isn't always the case, but it's a reasonable rule of thumb. It also doesn't mean that everything in that Received line is valid, any more than everything in the previous Received line was correct.
Spammers lie to everyone.
So let's look at the Received line filled in by the previous hop. And, as the Received line makes clear, that correct name differs wildly from the name handed to them by the sending system. People do give hosts and domains names like that in real life, but more often it's a spammer making something up. So the spamming host was almost certainly host4u.net. Neither is the listed subdomain, nada.kth.se.