Message for you, sir

After a long trek through the wilderness, the party makes it back to the watering hole at Flint Ridge.  Dirty and exhausted, they slump into their usual chairs.  There's a letter waiting for them with the tavern master.  The lieutenant digs out a shilling for it, then unfolds the letter.  Could it be news about the war?  Answers about the lost treasure?  A letter of credit to pay off the party's debts?

Ilya Repin, Reply of the Zaporozhian Cossacks

In a world where writing is magic, the post office is like the astral plane.  Secret messages, hidden money, many powerful things can be sent through the post office.

The colonial postal system almost didn't survive the apocalypse (hard to keep the mail going when no one's left to send any) but it's been a generation.  The viceroy, nominal ruler of the elven colonies, has reestablished post offices and messenger routes.  This is good for communication, but it also means the viceroy has agents visiting every major elven town, reporting back about the conditions and goings-on of the scattered colonies.

Getting a letter

In larger elven settlements there's a local post office.  Mail can be delivered to local addresses, though roving adventurers usually have things sent to the post office where they can pick them up.  Smaller outlying settlements aren't big enough for a post office, so there you can pick your mail up at the local tavern or the general store.

Unlike modern mail, in the colonies the recipient pays for correspondence.  If you don't pay for your mail, it ends up being thrown away.

Letters from another city cost a shilling (the usual small silver coin, worth half a day's wages or a ferry ride across a river).  Letters from across town cost only a penny or two.

Thomas Webster, A Letter from the Colonies

What they want (d6)
1	They want the party to do some work for them.
2	They want the party to stop interfering and go away.
3	They say the party owes them a debt.
4	They want to warn the party about danger.
5	They want information from the party.
6	They want to use one of the party's resources.

Why the party cares (d6)
1	They claim to be the authorities or powerful figures.
2	They have something the party wants.
3	They are offering to pay in some way.
4	The letter contains valuable information.
5	They are close to an enemy of the party.
6	The party owes them a debt.

a letter arrives for the party
what they want
why the party cares

Sending a letter

If you want to send a letter, there are a few different ways:

• Larger towns and cities have a post office, so you can drop your letter off there.
• In port towns, just hand your letter to the next ship captain headed to a major city.  They're supposed to drop it off with the postmaster when they arrive.
• Many inland settlements are visited by postal messengers on their route.  Wait for one to come along and you can hand your letter to them.
• You could entrust your letter with a member of the community (the innkeeper, the clerk of the general store, etc.) for them to hand off the letter for you.

So how long will it be till someone picks up your letter?

• From an elven city to the viceroy's capital in the Summer Isles (or vice versa), it'll be 1d6 days till a ship leaves carrying your letter.
• From one city to another, 1d4 weeks.
• To/from any other port settlement, 1d8 weeks.
• To/from any other elven settlement, 1d6 months.

Taconville, Messager Boiteaux

There are many reasons the party might send a letter:

• Asking for information: when a ship will sail, whether someone has been seen at an inn, where a lost ship was last seen, etc.
• Requesting money from their sponsor, likely in the form of a check or a letter of credit that could be turned in for coin at a bank.
• Mail ordering supplies.  Plenty of companies will do business through correspondence, shipping goods and accepting payment over a distance.
• Asking a friend for help.
• Impersonating someone powerful.
• Getting information published in a newspaper.
• Hiring someone to do a job.
• Blackmailing someone.
• Warning someone about danger.

Beyond the elven colonies and a few of their allies, the mail just doesn't get through.  Humans send runners with messages, giants memorize copious amounts of news on their wanderings, and goblins pass along a lot of garbled rumors.