"Elio" escribió en el mensaje
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I just received in the mail at home in Italy a speeding tickets that i
took
while driving a rental car in Spain last december. At that time i did not
realize i was doing such a violation and was not stopped by the police.
Also
no news from the car rental company. Does anyone have suggestions how to
handle it? What if i just ignore it?

I would ignore it. If I understand well, the ticket has been directly send
from the Direccion General de Trafico (kinda Secretary of Traffic), probably
because the car rental company gave your address, freeing themselves of any
responsibilities (in Spain, the car owner has to pay the fine unless he can
demonstrate that the driver was someone else). Had you been Spanish, the DGT
could have blocked one of your bank accounts until you pay the fine, but I
seriously doubt they can do that to an Italian citizen who has no bank
accounts in Spain (I suppose it is the case). The next time you come to
Spain, if a traffic policeman stops you, I seriously doubt you'd have a
problem because they don't have an online system to check if a foreigner has
pending fines or not.

Summarizing: when in Spain, if you are stopped by the traffic police and
fined, pay on the spot. If you receive a ticket after your trip, forget
about it.