SPRB!

I liked most of it but wasn't sure the element group really fit in, with both letters being capitalized.

I appreciated the descriptions here because I'd heard of a band called CSS but never CCS and initially wasn't sure it wasn't an error.

While not an English
river, SN could arguably swap with VN

Not often I get 10/10!

Liked this but rivers group would also make other words with two e's inserted.

Good stuff! I liked the rivers, I suppose you could say that rivers are normally contain water vowels.

Should accept "mail" for courier category

OK, I fell right into the trap: I got the rivers first due to SVRN, then assumed all the others were missing vowels as well (which obviously didn't get me very far). Nicely done.