diff --git a/src/core/http.ts b/src/core/http.ts
index 9685aff..8b64c86 100644
--- a/src/core/http.ts
+++ b/src/core/http.ts
@@ -29,20 +29,34 @@ export class HttpHandler {
         this.#baseUrl = props.urlEndpoint ?? DefaultEndpoint
     }
 
-    async get<T = unknown>(path: string, data?: unknown): Promise<T> {
+    async get<T = unknown>(path: string, data?: unknown): Promise<T | undefined> {
         return this.#request<T>('GET', path, data)
     }
 
-    async post<T = unknown>(path: string, data?: unknown): Promise<T> {
+    async post<T = unknown>(path: string, data?: unknown): Promise<T | undefined> {
         return this.#request<T>('POST', path, data)
     }
 
-    async delete<T = unknown>(path: string, data?: unknown): Promise<T> {
+    async delete<T = unknown>(path: string, data?: unknown): Promise<T | undefined> {
         return this.#request<T>('DELETE', path, data)
     }
 
-    async #request<T>(method: HttpMethod, path: string, data?: unknown): Promise<T> {
-        const url = `${this.#baseUrl}/client/${path}`
+    async #request<T>(method: HttpMethod, path: string, data?: unknown): Promise<T | undefined> {
+        let url = `${this.#baseUrl}/client/${path}`
+        let body: string | undefined
+
+        if (method === 'GET' && data) {
+            const mapped = mapKeys(data) as Record<string, unknown>
+            const params = new URLSearchParams()
+            for (const [key, value] of Object.entries(mapped)) {
+                if (value !== null && value !== undefined) {
+                    params.set(key, String(value))
+                }
+            }
+            url = `${url}?${params.toString()}`
+        } else if (data) {
+            body = JSON.stringify(mapKeys(data))
+        }
 
         try {
             const response = await fetch(url, {
@@ -51,7 +65,7 @@ export class HttpHandler {
                     'Content-Type': 'application/json',
                     'Authorization': `Bearer ${this.#apiKey}`,
                 },
-                body: data ? JSON.stringify(mapKeys(data)) : undefined,
+                body,
             })
 
             return this.#handleResponse<T>(response)
@@ -65,17 +79,22 @@ export class HttpHandler {
         }
     }
 
-    async #handleResponse<T>(response: Response): Promise<T> {
+    async #handleResponse<T>(response: Response): Promise<T | undefined> {
         if (!response.ok) {
             throw await this.#mapError(response)
         }
 
+        const contentLength = response.headers.get('content-length')
+        if (contentLength === '0') {
+            return undefined
+        }
+
         const contentType = response.headers.get('content-type')
         if (!contentType || !contentType.includes('application/json')) {
-            return undefined as T
+            return undefined
         }
 
-        return response.json() as Promise<T>
+        return response.json()
     }
 
     async #mapError(response: Response): Promise<LunogramError> {
diff --git a/src/core/resources/base.ts b/src/core/resources/base.ts
index 5f418bf..a8162e4 100644
--- a/src/core/resources/base.ts
+++ b/src/core/resources/base.ts
@@ -9,15 +9,15 @@ export abstract class BaseResource {
 
     protected abstract readonly endpoint: string
 
-    protected async get<T = unknown>(data?: unknown): Promise<T> {
-        return this.#http.get<T>(this.endpoint, data)
+    protected async get<T = unknown>(data?: unknown, pathOverride?: string): Promise<T | undefined> {
+        return this.#http.get<T>(pathOverride ?? this.endpoint, data)
     }
 
-    protected async post<T = unknown>(data?: unknown, pathOverride?: string): Promise<T> {
+    protected async post<T = unknown>(data?: unknown, pathOverride?: string): Promise<T | undefined> {
         return this.#http.post<T>(pathOverride ?? this.endpoint, data)
     }
 
-    protected async remove<T = unknown>(data?: unknown, pathOverride?: string): Promise<T> {
+    protected async remove<T = unknown>(data?: unknown, pathOverride?: string): Promise<T | undefined> {
         return this.#http.delete<T>(pathOverride ?? this.endpoint, data)
     }
 }
diff --git a/src/core/resources/organizations/events.ts b/src/core/resources/organizations/events.ts
index 8e7face..6a70c85 100644
--- a/src/core/resources/organizations/events.ts
+++ b/src/core/resources/organizations/events.ts
@@ -8,7 +8,7 @@ export class OrganizationEventsResource extends BaseResource {
      * Posts organization events for asynchronous processing.
      * @param data - Array of organization events
      */
-    async post<T = unknown>(data: OrganizationEvent[]): Promise<T> {
-        return super.post(data)
+    async post<T = unknown>(data: OrganizationEvent[]): Promise<T | undefined> {
+        return super.post<T>(data)
     }
 }
diff --git a/src/core/resources/organizations/inbox.ts b/src/core/resources/organizations/inbox.ts
new file mode 100644
index 0000000..aef8c0c
--- /dev/null
+++ b/src/core/resources/organizations/inbox.ts
@@ -0,0 +1,48 @@
+import { BaseResource } from '../base'
+import {
+    PostInboxMessagesRequest,
+    InboxMessageEvents,
+    GetInboxParams,
+    GetInboxCountParams,
+    InboxMessageList,
+    InboxCount,
+} from '../../../types'
+
+export class OrganizationInboxResource extends BaseResource {
+    readonly endpoint = 'organizations/inbox'
+
+    /**
+     * Creates one or more inbox messages for organizations. Processed asynchronously.
+     */
+    async create(data: PostInboxMessagesRequest): Promise<void> {
+        return super.post<void>(data)
+    }
+
+    /**
+     * Returns visible, non-expired inbox messages for an organization.
+     */
+    async list(params: GetInboxParams): Promise<InboxMessageList | undefined> {
+        return super.get<InboxMessageList>(params)
+    }
+
+    /**
+     * Returns unread and total inbox message counts for an organization.
+     */
+    async count(params: GetInboxCountParams): Promise<InboxCount | undefined> {
+        return super.get<InboxCount>(params, 'organizations/inbox/count')
+    }
+
+    /**
+     * Marks one or more inbox messages as opened. Processed asynchronously.
+     */
+    async opened(data: InboxMessageEvents): Promise<void> {
+        return super.post<void>(data, 'organizations/inbox/opened')
+    }
+
+    /**
+     * Marks one or more inbox messages as archived. Processed asynchronously.
+     */
+    async archived(data: InboxMessageEvents): Promise<void> {
+        return super.post<void>(data, 'organizations/inbox/archived')
+    }
+}
diff --git a/src/core/resources/organizations/index.ts b/src/core/resources/organizations/index.ts
index 237ff2c..50e521b 100644
--- a/src/core/resources/organizations/index.ts
+++ b/src/core/resources/organizations/index.ts
@@ -1,3 +1,4 @@
 export { OrganizationResource } from './organization'
 export { OrganizationScheduledResource } from './scheduled'
-export { OrganizationEventsResource } from './events'
\ No newline at end of file
+export { OrganizationEventsResource } from './events'
+export { OrganizationInboxResource } from './inbox'
\ No newline at end of file
diff --git a/src/core/resources/organizations/organization.ts b/src/core/resources/organizations/organization.ts
index 19b291a..e2d7d09 100644
--- a/src/core/resources/organizations/organization.ts
+++ b/src/core/resources/organizations/organization.ts
@@ -9,16 +9,19 @@ import { BaseResource } from "../base"
 import { HttpHandler } from "../../http"
 import { OrganizationScheduledResource } from "./scheduled"
 import { OrganizationEventsResource } from "./events"
+import { OrganizationInboxResource } from "./inbox"
 
 export class OrganizationResource extends BaseResource {
     readonly endpoint = 'organizations'
     readonly schedule: OrganizationScheduledResource
     readonly events: OrganizationEventsResource
+    readonly inbox: OrganizationInboxResource
 
     constructor(http: HttpHandler) {
         super(http)
         this.schedule = new OrganizationScheduledResource(http)
         this.events = new OrganizationEventsResource(http)
+        this.inbox = new OrganizationInboxResource(http)
     }
 
     /**
@@ -26,8 +29,8 @@ export class OrganizationResource extends BaseResource {
      * @param data - Organization data including identifier, name, data, etc.
      * @returns Promise resolving to the created/updated organization
      */
-    async upsert(data: OrganizationRequest): Promise<OrganizationResponse> {
-        return this.post(data)
+    async upsert(data: OrganizationRequest): Promise<OrganizationResponse | undefined> {
+        return this.post<OrganizationResponse>(data)
     }
 
     /**
@@ -36,7 +39,7 @@ export class OrganizationResource extends BaseResource {
      * @returns Promise resolving when organization is deleted
      */
     async delete(data: DeleteOrganizationRequest): Promise<void> {
-        return this.remove(data)
+        return this.remove<void>(data)
     }
 
     /**
@@ -45,7 +48,7 @@ export class OrganizationResource extends BaseResource {
      * @returns Promise resolving when user is added
      */
     async addUser(data: OrganizationUserRequest): Promise<void> {
-        return this.post(data, 'organizations/users')
+        return this.post<void>(data, 'organizations/users')
     }
 
     /**
@@ -54,6 +57,6 @@ export class OrganizationResource extends BaseResource {
      * @returns Promise resolving when user is removed
      */
     async removeUser(data: RemoveOrganizationUserRequest): Promise<void> {
-        return this.remove(data, 'organizations/users')
+        return this.remove<void>(data, 'organizations/users')
     }
 }
diff --git a/src/core/resources/organizations/scheduled.ts b/src/core/resources/organizations/scheduled.ts
index af2f77d..97d7f1f 100644
--- a/src/core/resources/organizations/scheduled.ts
+++ b/src/core/resources/organizations/scheduled.ts
@@ -16,8 +16,8 @@ export class OrganizationScheduledResource extends BaseResource {
      * @param data - Scheduled resource data including name, identifier, scheduledAt, interval, etc.
      * @returns Promise resolving to the accepted scheduled resource
      */
-    async upsert(data: UpsertOrganizationScheduledRequest): Promise<ScheduledAcceptedResponse> {
-        return this.post(data)
+    async upsert(data: UpsertOrganizationScheduledRequest): Promise<ScheduledAcceptedResponse | undefined> {
+        return this.post<ScheduledAcceptedResponse>(data)
     }
 
     /**
@@ -26,6 +26,6 @@ export class OrganizationScheduledResource extends BaseResource {
      * @returns Promise resolving when scheduled resource is deleted
      */
     async delete(data: DeleteOrganizationScheduledRequest): Promise<void> {
-        return this.remove(data)
+        return this.remove<void>(data)
     }
 }
diff --git a/src/core/resources/users/events.ts b/src/core/resources/users/events.ts
index 39c3c48..31b0d65 100644
--- a/src/core/resources/users/events.ts
+++ b/src/core/resources/users/events.ts
@@ -8,7 +8,7 @@ export class UserEventsResource extends BaseResource {
      * Posts user events for asynchronous processing.
      * @param data - Array of user events
      */
-    async post<T = unknown>(data: UserEvent[]): Promise<T> {
-        return super.post(data)
+    async post<T = unknown>(data: UserEvent[]): Promise<T | undefined> {
+        return super.post<T>(data)
     }
 }
diff --git a/src/core/resources/users/inbox.ts b/src/core/resources/users/inbox.ts
new file mode 100644
index 0000000..0db15a4
--- /dev/null
+++ b/src/core/resources/users/inbox.ts
@@ -0,0 +1,48 @@
+import { BaseResource } from '../base'
+import {
+    PostInboxMessagesRequest,
+    InboxMessageEvents,
+    GetInboxParams,
+    GetInboxCountParams,
+    InboxMessageList,
+    InboxCount,
+} from '../../../types'
+
+export class UserInboxResource extends BaseResource {
+    readonly endpoint = 'users/inbox'
+
+    /**
+     * Creates one or more inbox messages for users. Processed asynchronously.
+     */
+    async create(data: PostInboxMessagesRequest): Promise<void> {
+        return super.post<void>(data)
+    }
+
+    /**
+     * Returns visible, non-expired inbox messages for a user.
+     */
+    async list(params: GetInboxParams): Promise<InboxMessageList | undefined> {
+        return super.get<InboxMessageList>(params)
+    }
+
+    /**
+     * Returns unread and total inbox message counts for a user.
+     */
+    async count(params: GetInboxCountParams): Promise<InboxCount | undefined> {
+        return super.get<InboxCount>(params, 'users/inbox/count')
+    }
+
+    /**
+     * Marks one or more inbox messages as opened. Processed asynchronously.
+     */
+    async opened(data: InboxMessageEvents): Promise<void> {
+        return super.post<void>(data, 'users/inbox/opened')
+    }
+
+    /**
+     * Marks one or more inbox messages as archived. Processed asynchronously.
+     */
+    async archived(data: InboxMessageEvents): Promise<void> {
+        return super.post<void>(data, 'users/inbox/archived')
+    }
+}
diff --git a/src/core/resources/users/index.ts b/src/core/resources/users/index.ts
index aea3ac6..87b65fa 100644
--- a/src/core/resources/users/index.ts
+++ b/src/core/resources/users/index.ts
@@ -1,3 +1,4 @@
 export { UserResource } from './user'
 export { UserScheduledResource } from './scheduled'
-export { UserEventsResource } from './events'
\ No newline at end of file
+export { UserEventsResource } from './events'
+export { UserInboxResource } from './inbox'
\ No newline at end of file
diff --git a/src/core/resources/users/scheduled.ts b/src/core/resources/users/scheduled.ts
index bc033af..a25a597 100644
--- a/src/core/resources/users/scheduled.ts
+++ b/src/core/resources/users/scheduled.ts
@@ -16,8 +16,8 @@ export class UserScheduledResource extends BaseResource {
      * @param data - Scheduled resource data including name, identifier, scheduledAt, interval, etc.
      * @returns Promise resolving to the accepted scheduled resource
      */
-    async upsert(data: UpsertUserScheduledRequest): Promise<ScheduledAcceptedResponse> {
-        return this.post(data)
+    async upsert(data: UpsertUserScheduledRequest): Promise<ScheduledAcceptedResponse | undefined> {
+        return this.post<ScheduledAcceptedResponse>(data)
     }
 
     /**
@@ -26,6 +26,6 @@ export class UserScheduledResource extends BaseResource {
      * @returns Promise resolving when scheduled resource is deleted
      */
     async delete(data: DeleteUserScheduledRequest): Promise<void> {
-        return this.remove(data)
+        return this.remove<void>(data)
     }
 }
diff --git a/src/core/resources/users/user.ts b/src/core/resources/users/user.ts
index 5af36fb..dc3cfe5 100644
--- a/src/core/resources/users/user.ts
+++ b/src/core/resources/users/user.ts
@@ -7,16 +7,19 @@ import {
 } from '../../../types'
 import { UserScheduledResource } from './scheduled'
 import { UserEventsResource } from './events'
+import { UserInboxResource } from './inbox'
 
 export class UserResource extends BaseResource {
     readonly endpoint = 'users'
     readonly schedule: UserScheduledResource
     readonly events: UserEventsResource
+    readonly inbox: UserInboxResource
 
     constructor(http: HttpHandler) {
         super(http)
         this.schedule = new UserScheduledResource(http)
         this.events = new UserEventsResource(http)
+        this.inbox = new UserInboxResource(http)
     }
 
     /**
@@ -24,8 +27,8 @@ export class UserResource extends BaseResource {
      * @param data - User data including identifier, email, phone, etc.
      * @returns Promise resolving to the created/updated user
      */
-    async upsert(data: UpsertUserRequest): Promise<UserResponse> {
-        return this.post(data)
+    async upsert(data: UpsertUserRequest): Promise<UserResponse | undefined> {
+        return this.post<UserResponse>(data)
     }
 
     /**
@@ -34,6 +37,6 @@ export class UserResource extends BaseResource {
      * @returns Promise resolving when user is deleted
      */
     async delete(data: DeleteUserRequest): Promise<void> {
-        return this.remove(data)
+        return this.remove<void>(data)
     }
 }
diff --git a/src/platform/browser.ts b/src/platform/browser.ts
index 99e068c..91c11e0 100644
--- a/src/platform/browser.ts
+++ b/src/platform/browser.ts
@@ -24,14 +24,14 @@ class BrowserUserEventsResource extends UserEventsResource {
         this.#getIdentifier = getIdentifier
     }
 
-    async post<T = unknown>(data: UserEvent[]): Promise<T> {
+    async post<T = unknown>(data: UserEvent[]): Promise<T | undefined> {
         const identifier = this.#getIdentifier()
         const injected = data.map((event) => ({
             ...event,
             // Do not inject identifier when `match` is used (they are mutually exclusive)
             identifier: event.match ? event.identifier : (event.identifier ?? identifier),
         }))
-        return super.post(injected) as Promise<T>
+        return super.post<T>(injected)
     }
 }
 
@@ -43,7 +43,7 @@ class BrowserUserScheduledResource extends UserScheduledResource {
         this.#getIdentifier = getIdentifier
     }
 
-    async upsert(data: UpsertUserScheduledRequest): Promise<ScheduledAcceptedResponse> {
+    async upsert(data: UpsertUserScheduledRequest): Promise<ScheduledAcceptedResponse | undefined> {
         return super.upsert({
             ...data,
             identifier: data.identifier ?? this.#getIdentifier(),
@@ -113,7 +113,7 @@ class BrowserUserResource extends UserResource {
         return identifier
     }
 
-    async upsert(data: UpsertUserRequest): Promise<UserResponse> {
+    async upsert(data: UpsertUserRequest): Promise<UserResponse | undefined> {
         const identifier = this.#buildIdentifier(data.identifier)
         return super.upsert({ ...data, identifier })
     }
diff --git a/src/types/request.ts b/src/types/request.ts
index ee5dd5f..c670506 100644
--- a/src/types/request.ts
+++ b/src/types/request.ts
@@ -116,6 +116,68 @@ export interface RemoveOrganizationUserRequest {
     }
 }
 
+// Inbox types
+
+export type InboxStatus = 'unread' | 'opened' | 'archived'
+
+/** Request to create inbox messages */
+export interface PostInboxMessagesRequest {
+    source: string
+    externalId: string
+    messages: Record<string, JSONValue>[]
+}
+
+/** Request to mark inbox messages as opened or archived */
+export interface InboxMessageEvents {
+    source: string
+    externalId: string
+    messageIds: string[]
+}
+
+/** Query params for fetching inbox messages */
+export interface GetInboxParams {
+    source: string
+    externalId: string
+    channel: string
+    status?: InboxStatus
+    tags?: string
+    messageSource?: string
+    priority?: number
+    limit?: number
+    offset?: number
+}
+
+/** Query params for counting inbox messages */
+export interface GetInboxCountParams {
+    source: string
+    externalId: string
+    channel: string
+}
+
+/** A single inbox message as returned by the API */
+export interface InboxMessage {
+    id: string
+    data: Record<string, JSONValue>
+    status: InboxStatus
+    channel: string
+    priority: number
+    tags: string[]
+    createdAt: string
+    updatedAt: string
+}
+
+/** Paginated list of inbox messages */
+export interface InboxMessageList {
+    data: InboxMessage[]
+    total: number
+}
+
+/** Inbox message counts */
+export interface InboxCount {
+    unread: number
+    total: number
+}
+
 /** Event data for organization events */
 export interface OrganizationEvent {
     /** Organization identifier array. Mutually exclusive with `match`. */