The most important form of communication between player characters is in the form of messages. These represent letters, personal conversations and all other exchanges of words.
Like real-life conversations, messages can go to one or more readers/listeners/etc.
Every message is part of a conversation. These are basically convenient ways of grouping messages, like topics on a forum or threads in e-mail. Conversations have a topic or subject to help you sort things, and participants are set on the conversation, not for each individual message. You can also invite more participants into an existing conversation.
All the Realms also have a special realm-wide conversation where all members of the realm are automatically added (and removed, if they leave the realm). This is useful to reach everyone in the realm with a message.
Similarly, all Houses also have their own house-wide conversations.
Of special note is Local Conversations, which exist as unique per character, meaning you can only ever access your own copy of things. This also means you can actively trash messages from it without affecting what others have.
Conversations have their own unique permission system, and every character has permissions to every conversation (save for their own Local Conversation, which is handled separately).
Permissions track when a character joined a conversation, when they left a conversation, whether they can add or remove others, or whether they can grant permission to others to do so. For Realm and House conversations, this is handled by the game. Private conversations this is handled by whoever owns the conversation (usually, whoever started it).
Related, for Private Conversations, you can also opt to "Leave" the conversation on your own, ending your ability to receive new messages but retaining your access to ones you've seen. Alternatively, you can "Remove" a conversation, which will get rid of your access to it entirely, and trigger the game to prune it of messages that no one has access to see anymore.
When replying to a specific message, the game will show replies sorted under the message replied to so you can easily see what the sender is referring to. This makes it unnecessary in most cases to include quotes, which adds just so slightly to the atmosphere as people didn't generally quote in handwritten letters.
Along with the search boxes in the message writer that lets you do lookups, the game supports several other similar syntax links, as detailed below:
These links, along with the formatting guide below, should work in every text box in the game. If they don't, please let a developer know so we can fix it.
# Huge Header
## Large Header
*emphasis* -> emphasis
**strong emphasis** -> strong emphasis
***extra strong emphasis*** -> extra strong emphasis
make unordered lists by beginning each line with a single *
second-level sub unordered lists can be done with a space and then a * at the beginning of the line
...or numbered lists by using 1. 2. 3.
...but maybe you don't want a list, so add a \ after the number and before the period like this: 2015.
you can also blockquote a paragraph like this by leading with a >
...or even double or triple indent by adding more > symbols.
...or even add numbered or unordered lists in that block quote!