Hi! I wrote something on Cicero's use of correspondence here a while ago. As you'll see, Cicero talked quite a lot about mail.

I'm sure people in other states or civilizations would have other practices, and I will be interested in hearing about them from other posters.

EDIT: Ah hell, I'll just repost for convenience. I will note the conversation in the thread above was very useful and worth a read on its own. Lots of smart people asking and saying smart things. I think this post is the result of some 4 or 5 hours of questions and answers.

Probably we're out of luck on the "common man" bit. The level of literacy among the masses is hotly debated, never mind whether they sent thank you notes. Among the elite though, we have lots of evidence for private correspondence, and Cicero several times discusses how letters work. For instance[1] :

As to the frequency of my letters you have no ground for your complaint. The fact is our good sister Pomponia never informed me of there being a courier ready to take a letter. Farthermore, I never chanced to know of anyone going to Epirus, and I was not till recently informed of your being at Athens.

Edit: To those asking about professionalism of couriers, Cicero seems doubtful[2] :

I get letters from you far too seldom considering that you can much more easily find people starting for Rome than I to Athens : considering, too, that you are more certain of my being at Rome than I of your being at Athens. For instance, it is owing to this uncertainty on my part that this very letter is somewhat short, because not being sure as to where you are, I don't choose my confidential talk to fall into strange hands.

And this[3] :

I have now received three letters from you—one by the hands of M. Cornelius, which you gave him, I think, at Three Taverns; a second which your host at Canusium delivered to me; a third dated, according to you, from on board your pinnace, when the cable was already slipped. They were all three, to use a phrase from the schools of rhetoric flavoured with the salt of learning, and illumined with the marks of affection. In these letters, indeed, I am urgently pressed by you to send answers, but what renders me rather dilatory in this respect is the difficulty of finding a trustworthy carrier. How few of these gentry are able to convey a letter rather weightier than usual without lightening it by skimming its contents! Besides, I do not always care to send whenever anyone is starting for Epirus: for I suppose that, having offered victims before your Amaltheia, you at once started for the siege of Sicyon. And yet I am not even certain when you start to visit Antonius or how much time you are devoting to Epirus. Accordingly, I don't venture to trust either Achaeans or Epirotes with a letter somewhat more outspoken than usual. Now some events have occurred since you left me worth my writing to you, but they must not be trusted to the risk of a letter being lost, opened, or intercepted.

Couriers, even slaves, screwed up[4] :

When I had been eagerly expecting a letter from you as usual till evening, lo and behold a message that slaves have come from Rome. I summon them: I ask if they have any letters. "No," say they. "What do you say," said I, "nothing from Pomponius?" Frightened to death by my voice and look, they confessed that they had received one, and that it had been lost on the journey.

Letters could be delivered to the wrong address[5] :

What an abominable thing! No one gave you my letter written on the spot at Three Taverns in answer to your delightful letters! But the fact is that the packet into which I had put it arrived at my town house on the same day as I wrote it, and has been brought back to me to Formiae. Accordingly, I have directed the letter meant for you to be taken back again, to show you how pleased I was with yours.

But he trusted some couriers[6] :

This Cossinius, to whom I intrust my letter, seems to me a very good fellow, steady, devoted to you, and exactly the sort of man which your letter to me had described.

And when he was writing to Rome, he might trust just about anyone[7] :

I write this letter at four o'clock in the afternoon of the Cerealia (12th April), immediately after reading yours, but I shall despatch it, I think, tomorrow, by anyone I may chance to meet on the road.

Oh, to hell with it. I'm bored. Here's some more Cicero on the mail[8] :

"Being in my Tusculan villa" (that's for your "being in the Ceramicus")—however, I being there, a courier sent by your sister arrived from Rome and delivered me a letter from you, announcing at the same time that the courier who was going to you started that very afternoon. The result is that, though I do send an answer, I am forced by the shortness of the time to write only these few words.

Cicero also had a sort of book club by mail[9] :

I wish you would describe your Amaltheium to me, its decoration and its plan; and send me any poems or stories you may have about Amaltheia. I should like to make a copy of it at Arpinum. I will forward you something of what I have written. At present there is nothing finished.

And this (note, this "boy" was probably a slave. Haven't bothered to check the Latin):[10]

On the 1st of June, as I was on my way to Antium, and eagerly getting out of the way of M. Metellus's gladiators, your boy met me, and delivered to me a letter from you and a history of my consulship written in Greek.

Atticus had a forward button[11] :

Your letter, in which you inclose copies of his letters, has made me realize that my brother Quintus's feelings have undergone many alternations, and that his opinions and judgments have varied widely from time to time.