diff --git a/config/harness.yaml b/config/harness.yaml
index c1d5fa4..434c4b8 100644
--- a/config/harness.yaml
+++ b/config/harness.yaml
@@ -178,7 +178,8 @@ web:
   # The address to listen for requests on. Defaults to all addresses.
   # Be careful with this setting, as opening to the wide web will increase
   # your security perimeter.
-  address: localhost
+  # We listen on all in harness because we might be getting requests through the docker gateway.
+  address: "0.0.0.0"
 
   # A web API designed to intercept Matrix API
   # POST /_matrix/client/r0/rooms/{roomId}/report/{eventId}
@@ -186,3 +187,7 @@ web:
   abuseReporting:
     # Whether to enable this feature.
     enabled: true
+  # A web API for a description of all the combined rules from watched banlists.
+  # GET /api/1/ruleserver/updates
+  ruleServer:
+    enabled: false
diff --git a/src/Mjolnir.ts b/src/Mjolnir.ts
index 04d8def..82b3e3b 100644
--- a/src/Mjolnir.ts
+++ b/src/Mjolnir.ts
@@ -42,6 +42,7 @@ import { EventRedactionQueue, RedactUserInRoom } from "./queues/EventRedactionQu
 import * as htmlEscape from "escape-html";
 import { ReportManager } from "./report/ReportManager";
 import { WebAPIs } from "./webapis/WebAPIs";
+import RuleServer from "./models/RuleServer";
 
 export const STATE_NOT_STARTED = "not_started";
 export const STATE_CHECKING_PERMISSIONS = "checking_permissions";
@@ -144,7 +145,8 @@ export class Mjolnir {
         }
         await logMessage(LogLevel.INFO, "index", "Mjolnir is starting up. Use !mjolnir to query status.");
 
-        const mjolnir = new Mjolnir(client, managementRoomId, protectedRooms, banLists);
+        const ruleServer = config.web.ruleServer ? new RuleServer() : null;
+        const mjolnir = new Mjolnir(client, managementRoomId, protectedRooms, banLists, ruleServer);
         Mjolnir.addJoinOnInviteListener(mjolnir, client, config);
         return mjolnir;
     }
@@ -154,6 +156,8 @@ export class Mjolnir {
         public readonly managementRoomId: string,
         public readonly protectedRooms: { [roomId: string]: string },
         private banLists: BanList[],
+        // Combines the rules from ban lists so they can be served to a homeserver module or another consumer.
+        public readonly ruleServer: RuleServer|null,
     ) {
         this.explicitlyProtectedRoomIds = Object.keys(this.protectedRooms);
 
@@ -220,7 +224,7 @@ export class Mjolnir {
 
         // Setup Web APIs
         console.log("Creating Web APIs");
-        this.webapis = new WebAPIs(new ReportManager(this));
+        this.webapis = new WebAPIs(new ReportManager(this), this.ruleServer);
     }
 
     public get lists(): BanList[] {
@@ -431,6 +435,7 @@ export class Mjolnir {
         if (this.banLists.find(b => b.roomId === roomId)) return null;
 
         const list = new BanList(roomId, roomRef, this.client);
+        this.ruleServer?.watch(list);
         await list.updateList();
         this.banLists.push(list);
 
@@ -449,12 +454,14 @@ export class Mjolnir {
 
         const roomId = await this.client.resolveRoom(permalink.roomIdOrAlias);
         const list = this.banLists.find(b => b.roomId === roomId) || null;
-        if (list) this.banLists.splice(this.banLists.indexOf(list), 1);
+        if (list) {
+            this.banLists.splice(this.banLists.indexOf(list), 1);
+            this.ruleServer?.unwatch(list);
+        }
 
         await this.client.setAccountData(WATCHED_LISTS_EVENT_TYPE, {
             references: this.banLists.map(b => b.roomRef),
         });
-
         return list;
     }
 
@@ -508,6 +515,7 @@ export class Mjolnir {
             await this.warnAboutUnprotectedBanListRoom(roomId);
 
             const list = new BanList(roomId, roomRef, this.client);
+            this.ruleServer?.watch(list);
             await list.updateList();
             banLists.push(list);
         }
diff --git a/src/config.ts b/src/config.ts
index d1108e3..f97a85f 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -76,6 +76,9 @@ interface IConfig {
         abuseReporting: {
             enabled: boolean;
         }
+        ruleServer: {
+            enabled: boolean;
+        }
     }
 
     /**
@@ -137,7 +140,10 @@ const defaultConfig: IConfig = {
         address: "localhost",
         abuseReporting: {
             enabled: false,
-        }
+        },
+        ruleServer: {
+            enabled: false,
+        },
     },
 
     // Needed to make the interface happy.
diff --git a/src/models/BanList.ts b/src/models/BanList.ts
index c78a6ce..43463ef 100644
--- a/src/models/BanList.ts
+++ b/src/models/BanList.ts
@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import { extractRequestError, LogService, MatrixClient } from "matrix-bot-sdk";
+import { EventEmitter } from "events";
 import { ListRule } from "./ListRule";
 
 export const RULE_USER = "m.policy.rule.user";
@@ -70,11 +71,16 @@ export interface ListRuleChange {
     readonly previousState?: any,
 }
 
+declare interface BanList {
+    on(event: 'BanList.update', listener: (list: BanList, changes: ListRuleChange[]) => void): this
+    emit(event: 'BanList.update', list: BanList, changes: ListRuleChange[]): boolean
+}
+
 /**
  * The BanList caches all of the rules that are active in a policy room so Mjolnir can refer to when applying bans etc.
  * This cannot be used to update events in the modeled room, it is a readonly model of the policy room.
  */
-export default class BanList {
+class BanList extends EventEmitter {
     private shortcode: string|null = null;
     // A map of state events indexed first by state type and then state keys.
     private state: Map<string, Map<string, any>> = new Map();
@@ -86,6 +92,7 @@ export default class BanList {
      * @param client A matrix client that is used to read the state of the room when `updateList` is called.
      */
     constructor(public readonly roomId: string, public readonly roomRef, private client: MatrixClient) {
+        super();
     }
 
     /**
@@ -268,6 +275,9 @@ export default class BanList {
                 changes.push({rule, changeType, event, sender: event.sender, ... previousState ? {previousState} : {} });
             }
         }
+        this.emit('BanList.update', this, changes);
         return changes;
     }
 }
+
+export default BanList;
diff --git a/src/models/RuleServer.ts b/src/models/RuleServer.ts
new file mode 100644
index 0000000..ce41718
--- /dev/null
+++ b/src/models/RuleServer.ts
@@ -0,0 +1,319 @@
+/*
+Copyright 2019-2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+import BanList, { ChangeType, ListRuleChange, RULE_ROOM, RULE_SERVER, RULE_USER } from "./BanList"
+import * as crypto from "crypto";
+import { LogService } from "matrix-bot-sdk";
+import { ListRule } from "./ListRule";
+
+export const USER_MAY_INVITE = 'user_may_invite';
+export const CHECK_EVENT_FOR_SPAM = 'check_event_for_spam';
+
+/**
+ * Rules in the RuleServer format that have been produced from a single event.
+ */
+class EventRules {
+    constructor (
+        readonly eventId: string,
+        readonly roomId: string,
+        readonly ruleServerRules: RuleServerRule[],
+        // The token associated with when the event rules were created.
+        readonly token: number
+    ) {
+    }
+}
+
+/**
+ * A description of a property that should be checked as part of a RuleServerRule.
+ */
+interface Checks {
+    property: string;
+}
+
+/**
+ * A Rule served by the rule server.
+ */
+interface RuleServerRule {
+    // A unique identifier for this rule.
+    readonly id: string
+    // A description of a property that should be checked.
+    readonly checks: Checks
+}
+
+/**
+ * The RuleServer is an experimental server that is used to propogate the rules of the watched policy rooms (BanLists) to
+ * homeservers (or e.g. synapse modules).
+ * This is done using an experimental format that is heavily based on the "Spam Checker Callbacks" made available to
+ * synapse modules https://matrix-org.github.io/synapse/latest/modules/spam_checker_callbacks.html.
+ *
+ */
+export default class RuleServer {
+    // Each token is an index for a row of this two dimensional array.
+    // Each row represents the rules that were added during the lifetime of that token.
+    private ruleStartsByToken: EventRules[][] = [[]];
+
+    // Each row, indexed by a token, represents the rules that were stopped during the lifetime of that token.
+    private ruleStopsByToken: string[][] = [[]];
+
+    // We use this to quickly lookup if we have stored a policy without scanning rulesByToken.
+    // First key is the room id and the second is the event id.
+    private rulesByEvent: Map<string, Map<string, EventRules>> = new Map();
+
+    // A unique identifier for this server instance that is given to each response so we can tell if the token
+    // was issued by this server or not. This is important for when Mjolnir has been restarted
+    // but the client consuming the rules hasn't been
+    // and we need to tell the client we have rebuilt all of the rules (via `reset` in the response).
+    private readonly serverId: string = crypto.randomUUID();
+
+    // Represents the current instant in which rules can started and/or stopped.
+    // Should always be incremented before adding rules. See `nextToken`.
+    private currentToken = 0;
+
+    private readonly banListUpdateListener = this.update.bind(this);
+
+    /**
+     * The token is used to separate EventRules from each other based on when they were added.
+     * The lower the token, the longer a rule has been tracked for (relative to other rules in this RuleServer).
+     * The token is incremented before adding new rules to be served.
+     */
+    private nextToken(): void {
+        this.currentToken += 1;
+        this.ruleStartsByToken.push([]);
+        this.ruleStopsByToken.push([]);
+    }
+
+    /**
+     * Get a combination of the serverId and currentToken to give to the client.
+     */
+    private get since(): string {
+        return `${this.serverId}::${this.currentToken}`;
+    }
+
+    /**
+     * Get the `EventRules` object for a Matrix event.
+     * @param roomId The room the event came from.
+     * @param eventId The id of the event.
+     * @returns The `EventRules` object describing which rules have been created based on the policy the event represents
+     * or `undefined` if there are no `EventRules` associated with the event.
+     */
+    private getEventRules(roomId: string, eventId: string): EventRules|undefined {
+        return this.rulesByEvent.get(roomId)?.get(eventId);
+    }
+
+    /**
+     * Add the EventRule to be served by the rule server at the current token.
+     * @param eventRules Add rules for an associated policy room event. (e.g. m.policy.rule.user).
+     * @throws If there are already rules associated with the event specified in `eventRules.eventId`.
+     */
+    private addEventRules(eventRules: EventRules): void {
+        const {roomId, eventId, token} = eventRules;
+        if (this.rulesByEvent.get(roomId)?.has(eventId)) {
+            throw new TypeError(`There is already an entry in the RuleServer for rules created from the event ${eventId}.`);
+        }
+        const roomTable = this.rulesByEvent.get(roomId);
+        if (roomTable) {
+            roomTable.set(eventId, eventRules);
+        } else {
+            this.rulesByEvent.set(roomId, new Map().set(eventId, eventRules));
+        }
+        this.ruleStartsByToken[token].push(eventRules);
+    }
+
+    /**
+     * Stop serving the rules from this policy rule.
+     * @param eventRules The EventRules to stop serving from the rule server.
+     */
+    private stopEventRules(eventRules: EventRules): void {
+        const {eventId, roomId, token} = eventRules;
+        this.rulesByEvent.get(roomId)?.delete(eventId);
+        // We expect that each row of `rulesByEvent` list of eventRules (represented by 1 row in `rulesByEvent`) to be relatively small (1-5)
+        // as it can only contain eventRules added during the instant of time represented by one token.
+        const index = this.ruleStartsByToken[token].indexOf(eventRules);
+        if (index > -1) {
+            this.ruleStartsByToken[token].splice(index, 1);
+        }
+        eventRules.ruleServerRules.map(rule => this.ruleStopsByToken[this.currentToken].push(rule.id));
+    }
+
+    /**
+     * Update the rule server to reflect a ListRule change.
+     * @param change A ListRuleChange sourced from a BanList.
+     */
+    private applyRuleChange(change: ListRuleChange): void {
+        if (change.changeType === ChangeType.Added) {
+            const eventRules = new EventRules(change.event.event_id, change.event.room_id, toRuleServerFormat(change.rule), this.currentToken);
+            this.addEventRules(eventRules);
+        } else if (change.changeType === ChangeType.Modified) {
+            const entry: EventRules|undefined = this.getEventRules(change.event.roomId, change.previousState.event_id);
+            if (entry === undefined) {
+                LogService.error('RuleServer', `Could not find the rules for the previous modified state ${change.event['state_type']} ${change.event['state_key']} ${change.previousState?.event_id}`);
+                return;
+            }
+            this.stopEventRules(entry);
+            const eventRules = new EventRules(change.event.event_id, change.event.room_id, toRuleServerFormat(change.rule), this.currentToken);
+            this.addEventRules(eventRules);
+        } else if (change.changeType === ChangeType.Removed) {
+            // 1) When the change is a redaction, the original version of the event will be available to us in `change.previousState`.
+            // 2) When an event has been "soft redacted" (ie we have a new event with the same state type and state_key with no content),
+            // the events in the `previousState` and `event` slots of `change` will be distinct events.
+            // In either case (of redaction or "soft redaction") we can use `previousState` to get the right event id to stop.
+            const entry: EventRules|undefined = this.getEventRules(change.event.room_id, change.previousState.event_id);
+            if (entry === undefined) {
+                LogService.error('RuleServer', `Could not find the rules for the previous modified state ${change.event['state_type']} ${change.event['state_key']} ${change.previousState?.event_id}`);
+                return;
+            }
+            this.stopEventRules(entry);
+        }
+    }
+
+    /**
+     * Watch the ban list for changes and serve its policies as rules.
+     * You will almost always want to call this before calling `updateList` on the BanList for the first time,
+     * as we won't be able to serve rules that have already been interned in the BanList.
+     * @param banList a BanList to watch for rule changes with.
+     */
+    public watch(banList: BanList): void {
+        banList.on('BanList.update', this.banListUpdateListener);
+    }
+
+    /**
+     * Remove all of the rules that have been created from the policies in this banList.
+     * @param banList The BanList to unwatch.
+     */
+    public unwatch(banList: BanList): void {
+        banList.removeListener('BanList.update', this.banListUpdateListener);
+        const listRules = this.rulesByEvent.get(banList.roomId);
+        this.nextToken();
+        if (listRules) {
+            for (const rule of listRules.values()) {
+                this.stopEventRules(rule);
+            }
+        }
+    }
+
+    /**
+     * Process the changes that have been made to a BanList.
+     * This will ususally be called as a callback from `BanList.onChange`.
+     * @param banList The BanList that the changes happened in.
+     * @param changes An array of ListRuleChanges.
+     */
+    private update(banList: BanList, changes: ListRuleChange[]) {
+        if (changes.length > 0) {
+            this.nextToken();
+            changes.forEach(this.applyRuleChange, this);
+        }
+    }
+
+    /**
+     * Get all of the new rules since the token.
+     * @param sinceToken A token that has previously been issued by this server.
+     * @returns An object with the rules that have been started and stopped since the token and a new token to poll for more rules with.
+     */
+    public getUpdates(sinceToken: string | null): {start: RuleServerRule[], stop: string[], reset?: boolean, since: string} {
+        const updatesSince = <T = EventRules|string>(token: number | null, policyStore: T[][]): T[] => {
+            if (token === null) {
+                // The client is requesting for the first time, we will give them everything.
+                return policyStore.flat();
+            } else if (token === this.currentToken) {
+                // There will be no new rules to give this client, they're up to date.
+                return [];
+            } else {
+                return policyStore.slice(token).flat();
+            }
+        }
+        const [serverId, since] = sinceToken ? sinceToken.split('::') : [null, null];
+        const parsedSince: number | null = since ?  parseInt(since, 10) : null;
+        if (serverId && serverId !== this.serverId) {
+            // The server has restarted, but the client has not and still has rules we can no longer account for.
+            // So we have to resend them everything.
+            return {
+                start: updatesSince(null, this.ruleStartsByToken).map((e: EventRules) => e.ruleServerRules).flat(),
+                stop: updatesSince(null, this.ruleStopsByToken),
+                since: this.since,
+                reset: true
+            }
+        } else {
+            // We will bring the client up to date on the rules.
+            return {
+                start: updatesSince(parsedSince, this.ruleStartsByToken).map((e: EventRules) => e.ruleServerRules).flat(),
+                stop: updatesSince(parsedSince, this.ruleStopsByToken),
+                since: this.since,
+            }
+        }
+    }
+}
+
+/**
+* Convert a ListRule into the format that can be served by the rule server.
+* @param policyRule A ListRule to convert.
+* @returns An array of rules that can be served from the rule server.
+*/
+function toRuleServerFormat(policyRule: ListRule): RuleServerRule[] {
+   function makeLiteral(literal: string) {
+       return {literal}
+   }
+
+   function makeGlob(glob: string) {
+       return {glob}
+   }
+
+   function makeServerGlob(server: string) {
+       return {glob: `:${server}`}
+   }
+
+   function makeRule(checks: Checks) {
+       return {
+           id: crypto.randomUUID(),
+           checks: checks
+       }
+   }
+
+   if (policyRule.kind === RULE_USER) {
+       // Block any messages or invites from being sent by a matching local user
+       // Block any messages or invitations from being received that were sent by a matching remote user.
+       return [{
+           property: USER_MAY_INVITE,
+           user_id: [makeGlob(policyRule.entity)]
+       },
+       {
+           property: CHECK_EVENT_FOR_SPAM,
+           sender: [makeGlob(policyRule.entity)]
+       }].map(makeRule)
+   } else if (policyRule.kind === RULE_ROOM) {
+       // Block any messages being sent or received in the room, stop invitations being sent to the room and
+       // stop anyone receiving invitations from the room.
+       return [{
+           property: USER_MAY_INVITE,
+           'room_id': [makeLiteral(policyRule.entity)]
+       },
+       {
+           property: CHECK_EVENT_FOR_SPAM,
+           'room_id': [makeLiteral(policyRule.entity)]
+       }].map(makeRule)
+   } else if (policyRule.kind === RULE_SERVER) {
+       // Block any invitations from the server or any new messages from the server.
+       return [{
+           property: USER_MAY_INVITE,
+           user_id: [makeServerGlob(policyRule.entity)]
+       },
+       {
+           property: CHECK_EVENT_FOR_SPAM,
+           sender: [makeServerGlob(policyRule.entity)]
+       }].map(makeRule)
+   } else {
+       LogService.info('RuleServer', `Ignoring unsupported policy rule type ${policyRule.kind}`);
+       return []
+   }
+}
diff --git a/src/webapis/WebAPIs.ts b/src/webapis/WebAPIs.ts
index 9d7487a..ded0f3b 100644
--- a/src/webapis/WebAPIs.ts
+++ b/src/webapis/WebAPIs.ts
@@ -17,11 +17,13 @@ limitations under the License.
 import { Server } from "http";
 
 import * as express from "express";
-import { MatrixClient } from "matrix-bot-sdk";
+import { LogService, MatrixClient } from "matrix-bot-sdk";
 
 import config from "../config";
+import RuleServer from "../models/RuleServer";
 import { ReportManager } from "../report/ReportManager";
 
+
 /**
  * A common prefix for all web-exposed APIs.
  */
@@ -33,7 +35,7 @@ export class WebAPIs {
     private webController: express.Express = express();
     private httpServer?: Server;
 
-    constructor(private reportManager: ReportManager) {
+    constructor(private reportManager: ReportManager, private readonly ruleServer: RuleServer|null) {
         // Setup JSON parsing.
         this.webController.use(express.json());
     }
@@ -56,6 +58,22 @@ export class WebAPIs {
             });
             console.log(`Configuring ${API_PREFIX}/report/:room_id/:event_id... DONE`);
         }
+
+        // Configure ruleServer API.
+        // FIXME: Doesn't this need some kind of access control?
+        // See https://github.com/matrix-org/mjolnir/issues/139#issuecomment-1012221479.
+        if (config.web.ruleServer.enabled) {
+            const updatesUrl = `${API_PREFIX}/ruleserver/updates`;
+            LogService.info("WebAPIs", `Configuring ${updatesUrl}...`);
+            if (!this.ruleServer) {
+                throw new Error("The rule server to use has not been configured for the WebAPIs.");
+            }
+            const ruleServer: RuleServer = this.ruleServer;
+            this.webController.get(updatesUrl, async (request, response) => {
+                await this.handleRuleServerUpdate(ruleServer, { request, response, since: request.query.since as string});
+            });
+            LogService.info("WebAPIs", `Configuring ${updatesUrl}... DONE`);
+        }
     }
 
     public stop() {
@@ -163,4 +181,16 @@ export class WebAPIs {
             response.status(503);
         }
     }
+
+    async handleRuleServerUpdate(ruleServer: RuleServer, { since, request, response }: { since: string, request: express.Request, response: express.Response }) {
+        // FIXME Have to do this because express sends keep alive by default and during tests.
+        // The server will never be able to close because express never closes the sockets, only stops accepting new connections.
+        // See https://github.com/matrix-org/mjolnir/issues/139#issuecomment-1012221479.
+        response.set("Connection", "close");
+        try {
+            response.json(ruleServer.getUpdates(since)).status(200);
+        } catch (ex) {
+            LogService.error("WebAPIs", `Error responding to a rule server updates request`, since, ex);
+        }
+    }
 }
diff --git a/test/integration/commands/commandUtils.ts b/test/integration/commands/commandUtils.ts
index c1839a3..4c3a89d 100644
--- a/test/integration/commands/commandUtils.ts
+++ b/test/integration/commands/commandUtils.ts
@@ -1,4 +1,52 @@
 import { MatrixClient } from "matrix-bot-sdk";
+import { strict as assert } from "assert";
+import * as crypto from "crypto";
+
+/**
+ * Returns a promise that resolves to the first event replying to the event produced by targetEventThunk.
+ * @param client A MatrixClient that is already in the targetRoom. We will use it to listen for the event produced by targetEventThunk.
+ * This function assumes that the start() has already been called on the client.
+ * @param targetRoom The room to listen for the reply in.
+ * @param targetEventThunk A function that produces an event ID when called. This event ID is then used to listen for a reply.
+ * @returns The replying event.
+ */
+ export async function getFirstReply(client: MatrixClient, targetRoom: string, targetEventThunk: () => Promise<string>): Promise<any> {
+    let reactionEvents = [];
+    const addEvent = function (roomId, event) {
+        if (roomId !== targetRoom) return;
+        if (event.type !== 'm.room.message') return;
+        reactionEvents.push(event);
+    };
+    let targetCb;
+    try {
+        client.on('room.event', addEvent)
+        const targetEventId = await targetEventThunk();
+        for (let event of reactionEvents) {
+            const in_reply_to = event.content['m.relates_to']?.['m.in_reply_to'];
+            if (in_reply_to.event_id === targetEventId) {
+                return event;
+            }
+        }
+        return await new Promise(resolve => {
+            targetCb = function(roomId, event) {
+                if (roomId !== targetRoom) return;
+                if (event.type !== 'm.room.message') return;
+                const in_reply_to = event.content['m.relates_to']?.['m.in_reply_to'];
+                if (in_reply_to?.event_id === targetEventId) {
+                    resolve(event)
+                }
+            }
+            client.on('room.event', targetCb);
+        });
+    } finally {
+        client.removeListener('room.event', addEvent);
+        if (targetCb) {
+            client.removeListener('room.event', targetCb);
+        }
+    }
+}
+
+
 
 /**
  * Returns a promise that resolves to an event that is reacting to the event produced by targetEventThunk.
@@ -9,7 +57,7 @@ import { MatrixClient } from "matrix-bot-sdk";
  * @param targetEventThunk A function that produces an event ID when called. This event ID is then used to listen for a reaction.
  * @returns The reaction event.
  */
-export async function onReactionTo(client: MatrixClient, targetRoom: string, reactionKey: string, targetEventThunk: () => Promise<string>): Promise<any> {
+export async function getFirstReaction(client: MatrixClient, targetRoom: string, reactionKey: string, targetEventThunk: () => Promise<string>): Promise<any> {
     let reactionEvents = [];
     const addEvent = function (roomId, event) {
         if (roomId !== targetRoom) return;
@@ -44,3 +92,19 @@ export async function onReactionTo(client: MatrixClient, targetRoom: string, rea
         }
     }
 }
+
+/**
+ * Create a new banlist for mjolnir to watch and return the shortcode that can be used to refer to the list in future commands.
+ * @param managementRoom The room to send the create command to.
+ * @param mjolnir A syncing matrix client.
+ * @param client A client that isn't mjolnir to send the message with, as you will be invited to the room.
+ * @returns The shortcode for the list that can be used to refer to the list in future commands.
+ */
+export async function createBanList(managementRoom: string, mjolnir: MatrixClient, client: MatrixClient): Promise<string> {
+    const listName = crypto.randomUUID();
+    const listCreationResponse = await getFirstReply(mjolnir, managementRoom, async () => {
+        return await client.sendMessage(managementRoom, { msgtype: 'm.text', body: `!mjolnir list create ${listName} ${listName}`});
+    });
+    assert.equal(listCreationResponse.content.body.includes('This list is now being watched.'), true, 'could not create a list to test with.');
+    return listName;
+}
diff --git a/test/integration/commands/redactCommandTest.ts b/test/integration/commands/redactCommandTest.ts
index 153abab..3971e0d 100644
--- a/test/integration/commands/redactCommandTest.ts
+++ b/test/integration/commands/redactCommandTest.ts
@@ -4,7 +4,7 @@ import config from "../../../src/config";
 import { newTestUser } from "../clientHelper";
 import { getMessagesByUserIn } from "../../../src/utils";
 import { LogService } from "matrix-bot-sdk";
-import { onReactionTo } from "./commandUtils";
+import { getFirstReaction } from "./commandUtils";
 
  describe("Test: The redaction command", function () {
     it('Mjölnir redacts all of the events sent by a spammer when instructed to by giving their id and a room id.', async function() {
@@ -34,7 +34,7 @@ import { onReactionTo } from "./commandUtils";
 
         try {
             moderator.start();
-            await onReactionTo(moderator, this.mjolnir.managementRoomId, '✅', async () => {
+            await getFirstReaction(moderator, this.mjolnir.managementRoomId, '✅', async () => {
                 return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir redact ${badUserId} ${targetRoom}` });
             });
         } finally {
@@ -81,7 +81,7 @@ import { onReactionTo } from "./commandUtils";
 
         try {
             moderator.start();
-            await onReactionTo(moderator, this.mjolnir.managementRoomId, '✅', async () => {
+            await getFirstReaction(moderator, this.mjolnir.managementRoomId, '✅', async () => {
                 return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir redact ${badUserId}` });
             });
         } finally {
@@ -117,7 +117,7 @@ import { onReactionTo } from "./commandUtils";
 
         try {
             moderator.start();
-            await onReactionTo(moderator, this.mjolnir.managementRoomId, '✅', async () => {
+            await getFirstReaction(moderator, this.mjolnir.managementRoomId, '✅', async () => {
                 return await moderator.sendMessage(this.mjolnir.managementRoomId, {msgtype: 'm.text', body: `!mjolnir redact https://matrix.to/#/${encodeURIComponent(targetRoom)}/${encodeURIComponent(eventToRedact)}`});
             });
         } finally {
diff --git a/test/integration/policyConsumptionTest.ts b/test/integration/policyConsumptionTest.ts
new file mode 100644
index 0000000..1b6a405
--- /dev/null
+++ b/test/integration/policyConsumptionTest.ts
@@ -0,0 +1,151 @@
+import { strict as assert } from "assert";
+
+import { newTestUser } from "./clientHelper";
+import { getMessagesByUserIn } from "../../src/utils";
+import config from "../../src/config";
+import axios from "axios";
+import { LogService } from "matrix-bot-sdk";
+import { createBanList, getFirstReaction } from "./commands/commandUtils";
+
+/**
+ * Get a copy of the rules from the ruleserver.
+ */
+async function currentRules() {
+    return await (await axios.get(`http://${config.web.address}:${config.web.port}/api/1/ruleserver/updates/`)).data
+}
+
+/**
+ * Wait for the rules to change as a result of the thunk. The returned promise will resolve when the rules being served have changed.
+ * @param thunk Should cause the rules the RuleServer is serving to change some way.
+ */
+async function waitForRuleChange(thunk): Promise<void> {
+    const initialRules = await currentRules();
+    let rules = initialRules;
+    // We use JSON.stringify like this so that it is pretty printed in the log and human readable.
+    LogService.debug('policyConsumptionTest', `Rules before we wait for them to change: ${JSON.stringify(rules, null, 2)}`);
+    await thunk();
+    while (rules.since === initialRules.since) {
+        await new Promise<void>(resolve => {
+            setTimeout(resolve, 500);
+        })
+        rules = await currentRules();
+    };
+    // The problem is, we have no idea how long a consumer will take to process the changed rules.
+    // We know the pull peroid is 1 second though.
+    await new Promise<void>(resolve => {
+        setTimeout(resolve, 1500);
+    })
+    LogService.debug('policyConsumptionTest', `Rules after they have changed: ${JSON.stringify(rules, null, 2)}`);
+}
+
+describe("Test: that policy lists are consumed by the associated synapse module", function () {
+    this.afterEach(async function () {
+        if(config.web.ruleServer.enabled) {
+            this.timeout(5000)
+            LogService.debug('policyConsumptionTest', `Rules at end of test ${JSON.stringify(await currentRules(), null, 2)}`);
+            const mjolnir = config.RUNTIME.client!;
+            // Clear any state associated with the account.
+            await mjolnir.setAccountData('org.matrix.mjolnir.watched_lists', {
+                references: [],
+            });
+        }
+    })
+    this.beforeAll(async function() {
+        if (!config.web.ruleServer.enabled) {
+            LogService.warn("policyConsumptionTest", "Skipping policy consumption test because the ruleServer is not enabled")
+            this.skip();
+        }
+    })
+    this.beforeEach(async function () {
+        this.timeout(1000);
+        const mjolnir = config.RUNTIME.client!;
+    })
+    it('blocks users in antispam when they are banned from sending messages and invites serverwide.', async function() {
+        this.timeout(20000);
+        // Create a few users and a room.
+        let badUser = await newTestUser(false, "spammer");
+        let badUserId = await badUser.getUserId();
+        const mjolnir = config.RUNTIME.client!
+        let mjolnirUserId = await mjolnir.getUserId();
+        let moderator = await newTestUser(false, "moderator");
+        this.moderator = moderator;
+        await moderator.joinRoom(this.mjolnir.managementRoomId);
+        let unprotectedRoom = await badUser.createRoom({ invite: [await moderator.getUserId()]});
+        // We do this so the moderator can send invites, no other reason.
+        await badUser.setUserPowerLevel(await moderator.getUserId(), unprotectedRoom, 100);
+        await moderator.joinRoom(unprotectedRoom);
+        const banList = await createBanList(this.mjolnir.managementRoomId, mjolnir, moderator);
+        await badUser.sendMessage(unprotectedRoom, {msgtype: 'm.text', body: 'Something bad and mean'});
+
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir ban ${banList} ${badUserId}` });
+            });
+        });
+        await assert.rejects(badUser.sendMessage(unprotectedRoom, { msgtype: 'm.text', body: 'test'}), 'The bad user should be banned and unable to send messages.');
+        await assert.rejects(badUser.inviteUser(mjolnirUserId, unprotectedRoom), 'They should also be unable to send invitations.');
+        assert.ok(await moderator.inviteUser('@test:localhost:9999', unprotectedRoom), 'The moderator is not banned though so should still be able to invite');
+        assert.ok(await moderator.sendMessage(unprotectedRoom, { msgtype: 'm.text', body: 'test'}), 'They should be able to send messages still too.');
+
+        // Test we can remove the rules.
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir unban ${banList} ${badUserId}` });
+            });
+        });
+        assert.ok(await badUser.sendMessage(unprotectedRoom, { msgtype: 'm.text', body: 'test'}));
+        assert.ok(await badUser.inviteUser(mjolnirUserId, unprotectedRoom));
+    })
+    it('Test: Cannot send message to a room that is listed in a policy list and cannot invite a user to the room either', async function () {
+        this.timeout(20000);
+        let badUser = await newTestUser(false, "spammer");
+        const mjolnir = config.RUNTIME.client!
+        let moderator = await newTestUser(false, "moderator");
+        await moderator.joinRoom(this.mjolnir.managementRoomId);
+        const banList = await createBanList(this.mjolnir.managementRoomId, mjolnir, moderator);
+        let badRoom = await badUser.createRoom();
+        let unrelatedRoom = await badUser.createRoom();
+        await badUser.sendMessage(badRoom, {msgtype: 'm.text', body: "Very Bad Stuff in this room"});
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir ban ${banList} ${badRoom}` });
+            });
+        });
+        await assert.rejects(badUser.sendMessage(badRoom, { msgtype: 'm.text', body: 'test'}), 'should not be able to send messagea to a room which is listed.');
+        await assert.rejects(badUser.inviteUser(await moderator.getUserId(), badRoom), 'should not be able to invite people to a listed room.');
+        assert.ok(await badUser.sendMessage(unrelatedRoom, { msgtype: 'm.text.', body: 'hey'}), 'should be able to send messages to unrelated room');
+        assert.ok(await badUser.inviteUser(await moderator.getUserId(), unrelatedRoom), 'They should still be able to invite to other rooms though');
+        // Test we can remove these rules.
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir unban ${banList} ${badRoom}` });
+            });
+        });
+
+        assert.ok(await badUser.sendMessage(badRoom, { msgtype: 'm.text', body: 'test'}), 'should now be able to send messages to the room.');
+        assert.ok(await badUser.inviteUser(await moderator.getUserId(), badRoom), 'should now be able to send messages to the room.');
+    })
+    it('Test: When a list becomes unwatched, the associated policies are stopped.', async function () {
+        this.timeout(20000);
+        const mjolnir = config.RUNTIME.client!
+        let moderator = await newTestUser(false, "moderator");
+        await moderator.joinRoom(this.mjolnir.managementRoomId);
+        const banList = await createBanList(this.mjolnir.managementRoomId, mjolnir, moderator);
+        let targetRoom = await moderator.createRoom();
+        await moderator.sendMessage(targetRoom, {msgtype: 'm.text', body: "Fluffy Foxes."});
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir ban ${banList} ${targetRoom}` });
+            });
+        });
+        await assert.rejects(moderator.sendMessage(targetRoom, { msgtype: 'm.text', body: 'test'}), 'should not be able to send messages to a room which is listed.');
+
+        await waitForRuleChange(async () => {
+            await getFirstReaction(mjolnir, this.mjolnir.managementRoomId, '✅', async () => {
+                return await moderator.sendMessage(this.mjolnir.managementRoomId, { msgtype: 'm.text', body: `!mjolnir unwatch #${banList}:localhost:9999` });
+            });
+        });
+
+        assert.ok(await moderator.sendMessage(targetRoom, { msgtype: 'm.text', body: 'test'}), 'should now be able to send messages to the room.');
+    })
+});