[renekooi]

Messages are sent through plainly first over Twitch's IRC-ish protocol. You can connect to Twitch chat with a simple IRC client, or through the browser. Twitch's own browser chat connects to a WebSocket server that passes IRC commands to the browser, where they are parsed & executed.

Twitch has a few additional IRC-ish commands like CLEARCHAT, which deletes messages by a given user. Most IRC clients don't support this, but Twitch's browser client of course does :) In larger streams spammy messages are usually removed by bots like http://www.nightbot.tv/ or http://twitch.moobot.tv/. That's where the delay comes from: messages have to arrive at the moderator first.

Interestingly, CLEARCHAT can only delete _all_ messages by a given user (as far as I know), so non-offending messages are also removed. This is done by the client, the chat servers only pass "CLEARCHAT #channel_name user_name". (e; it's all messages by a given user, or all messages in the channel if no username is given)

In the Twitch browser client, you can double-click the <message deleted> text to show the original text if you really want to! :)

Reference: https://github.com/justintv/Twitch-API/blob/master/IRC.md