Postal Service in 1st Century Roman Empire?

I was reflecting upon last Sunday’s epistle reading (Paul’s letter to the Thessalonians), at Mass.
Assuming that St. Paul wrote this letter, and that he did so while residing in Asia Minor (Patmos, perhaps?), how long would it take his letter to reach Thessalonika?
Was there regular post service? I know that the Roman Army/Government had its own system of couriers for official mail-was there any such mail system for private citizens?
Or wold Paul’setter be carried by a dedicated corier?

No government-run system in the Empire nor Republic, sorry.
Except for Official Government-only messenger riders.
Merchants would contract to carry private messages, for a fee.

Though obviously non-official messages were common. The Vindolanda tablets for example contain plenty of personal correspondence in addition to official business. I assume the personal letters were carried by the same messenger service as the office ones.

I cannot say how verified this is, but in reading the eminent and apparently well researched Masters of Rome series by Colleen McCullough, frequent mentions are made in letters written by the main characters, that they have to hurry up finishing the letter due to official couriers leaving to/from Rome soon. My understanding based on this is that couriers would frequently carry private correspondence, at least from high ranking Romans, and that these couriers would make fairly regular runs between important cities and Rome.

Based on the sheer numbers of letters that would have to criss cross the Empire on a regular basis to conduct diplomacy, warfare and not least the huge amounts of business transactions, I assume there were quite well established routes mail could travel by - be it official couriers, or private enterprises.

There were, after all, private companies in Rome operating mines in Spain, buying grain in Egypt, organizing the import of slaves from Greece. All this would require a fairly regular “postal” service, I would imagine.

Edited to add - The Cursus Puplicus, or the official postal system, was started during the reign of Augustus, wheter it had been opened up for private use by the time of Paul, I don’t know.

To late to edit:

According to this the postal service wasn’t opened to private parties until the 3rd Century, previously one would have to rely on slaves or merchants to get a message across.

I guess a lot of high ranking Romans/businesses would be able to use the official system, but probably not someone like Paul. He would most likely have rented a courier or got a merchant vessel to carry it. Seeing as there was alot of small vessel traffic across the Aegan Sea, I couldnt imagine it would take more than a week or two to find a suitable vessel going more or less to the right destination, and the trip itself wouldn’t take more than two-three days, assuming reasonable weather.

IIRC from various historical novels, the idea was to find a ship or caravan or whatever going the right destination and give the message to the captain/leader. If the destination was inland from the next port, usually you would have a contact or friend who would accept the message from the captain and make the arrangements to forward it on the next leg.

Keep in mind that most “cities” in Roman times were essentially small towns. The people who needed to send letters were usually the elite; they all knew each other, and people of a common ethnic backgrond or tribe stuck together because they could only trust each other. The 20th-century conceit of “privacy” did not exist; everyone gossiped and everyone knew everyone else’s business, like any small town; and a household of any size had sevants and slaves who gossiped with the neighbours too. Plus, there were no autos, so odds are anyone you needed to send a message to lived within walking distance of the docks. If it was a fellow merchant, not somebody too hoity-toity noble, I bet the captain could also wangle a free dinner invitation out of the deal, and make some more contacts for cargo. Win-win.

If you were a noble or very rich and the letter contents were important, you could afford to send someone on the voyage to deliver it. Odds are they got a full bag and delivered more than one item if it was a long journey. If your friends knew you one of your men headed for your estates back home, they would probably dump some extra correspondence on you. When not in ROme, quid pro quo.

… Like Rosencratz and Guildernstern, if you had someone going that way and you gave them a letter to deliver, just make sure you sealed it well with a good sealing wax.

Another problem - sealing was common because otherwise nosey Parkers would read it. Or worse… In “The Lisle Letter”, it was mentioned that part of the run-on sentence structure in Tudor correspondence was based on a simple rule - if you left blank space, you ran the risk that someone would forge extra items into the letter if they had a motive to frame you.

St Paul’s letter to the Corinthians, the background story.