Two stamps today, one later
A Thai office reads the consular stamp, not the Italian one on its own, and that is why the chain has two links today. Thailand has acceded to the Hague Apostille Convention with an entry into force of 28 February 2027. Until then a paper leaving Messina is legalised in Italy and then attested by Thailand's mission here.
The Messina to Thailand route step by step
Work out first which office owns your paper. Records from a comune, a school, a hospital or the police go to the Prefettura, the state's office in the province. Papers from a court, and deeds a notary has drawn up, go to the Procura della Repubblica at the courthouse. The stamp they apply is the same in either case, and so is the €16 tax stamp that pays for it.
What it costs and how long it takes
Two charges sit on this route. The Italian one is fixed and published at €16 for each document, with a handful of exempt kinds. The Thai mission sets the other at its own end, so budget for an official fee there as well. Timing depends on both desks, which is why a firm date is worth more to you than a fast one.
Planning around 28 February 2027
The apostille requirements for Thailand from that date are the Italian steps and nothing after them. If your file is due well past the switch, waiting cuts a whole leg out of the journey. If it is due before, the two-stamp route is the only one that works, and starting early is worth more than any short cut.