419s in mail...
...usually use counterfeit stamps. Take a closer look and/or complain to your local postal inspector.
This is why the USA blocked all paper mail from Nigeria for a while - sourcing postal countries pay around 1/3 of the face value of stamps to the destination postal country for final delivery. Something like 2/3 of all the mail coming in from Nigeria had fake stamps which Nigeria Post wouldn't pay for.
The Yahoo case is civil. They can now track/trace the sources and apply to courts local to the miscreants for enforcement. 90% of such applications are sucessful, but collection is still problematic.
Personally: I won't be removing my Yahoo email block anytime soon. They may have won a case but the level of inbound traffic to trap addresses remains constant (these are (of course) let through to feed filters.)
If the UK was serious about stopping 419-type scams then Ofcom would take steps to shut down the 070* "personal follow me" services(*) as IME 90% of the are used fraudulently and victims can be charged up to 1.50 per minute to call them. (businesses using 070* is just as fraudulent as a 419er. The service is supposed to be _personal_ numbers. Ditto any entity which claims "this is a mobile phone")
(*) They've floated doing this a few times, with the inevitable outcry from the 2 dozen companies which provide 070* service. Companies which tend to the shady side as a rule.