Not that I agree with this ban. I really don’t but focusing on farmers specifically is very strange when farming is so heavily commercialized, especially in the Netherlands.
This is as old as countries themselves. You must be intellectually dishonest to ignore these historically crucial patterns.
But yeah, if you’re not a citizen and don’t live in the EU it might be tricky (then again AFAIK bringing large amounts of cash from a third country is not that straightforward either).
What does this have to do with Dutch farmers, though?
For paper mails some shelters allow for picking up post and in some countries you can get the mail as "Poste Restante" (i.e. pick up at post office).
Also, again, how is this specifically harming farmers more than anyone else?