Hello from Italy :-)
I'm sorry that you received this bad gift after your trip. Shortly answer I suggest you to ignore this, as can't be enforced in UK, and will not be enforced. They will only try to stress you/scare you with reminders / credit collectors letters for a while (credit collectors not bailiffs).
Italian Traffic Fines (both parking and moving ones) are only civil matters and you will have no consequences even in the case you will come back to Italy (there are only few exceptions to this for very serious matters like driving under alcohol/drugs or running away from a car accident or other few very serious matters: these are criminal offences and are registered in your records).
Rental company never directly pay traffic tickets in Italy: they simply have to send to the police/municipality the renter's name and address and then is up to the police / council to chase you. For doing this rental companies always charge you an admin fee (and surely they have already charged your credit card, normally something around 50 Euros, sometimes more. It's written in the rental agreement).
Why I'm telling you this? Not because I'm an Italian that likes foreigners coming to Italy doing what they want, but because you probably made an honest error, entering in a city center zone closed to traffic and got caught by a camera, maybe bad signposted like often happens. This zones are very common in Italy but unusual for many foreigners.
And for this honest error they are trying to charge you in an indecent way. For that violation the fine is 58 Euros if paid in 5 days from when you receive it or 83 Euro if paid from 5 to 60 days from when you receive.
Italian law says that they can add on the top of the fine the expenses that they have to notify you the report. But guys, here they are trying to charge you around 60 Euros!!! For what? For sending you a letter at the address received from the rental company? The fact is that there are a lot of municipality that are "outsourcing" fine management to be sent abroad to external companies, like the one that wrote to you, that work for free (for the municipality) but they are "allowed" to charge whatever they want on the top. There have been different scandals about this kind of companies in Italy and I simply find that this is a shame.
Plus I'm not a native English speaker but I have never seen a translation bad as that. There are also a lot of technical errors like, for example, its the owner or the renter that is responsible for payment not the driver, they are not detailing the amount of the fine and the amount of the expenses as the law requires (guess why...), they declare that they have sent the letter from a Vatican Post Office (not joking read among the lines, never seen this but Vatican is not Italy and they have to send the letter from Italy according to the law. Never seen this, maybe Vatican Post Service is less expensive than the Italian one). Never seen a **** like that. Do you what to gain 60 Euros of expenses? At least do a decent job...
As said I'm a very law obeying citizen, in Italy and abroad but I don't like to see a tourist "scammed" in this way for a simply honest mistake.
Hope you liked my country as I liked your during my different trips :-)