> For the complete documentation index, see [llms.txt](https://brightercommand.gitbook.io/paramore-brighter-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://brightercommand.gitbook.io/paramore-brighter-documentation/outbox-and-inbox/brighterinboxsupport/inmemoryinbox.md).

# InMemory Inbox

The in-process Inbox: when to use it, how to configure it, and its limits.

> **Reference** · Applies to **Brighter V10** · Prerequisites: [InMemory Options for Development and Testing](/paramore-brighter-documentation/brighter-configuration/inmemoryoptions.md)

The in-process Inbox: when to use it, how to configure it, and its limits. It is part of Brighter's [InMemory options for development and testing](/paramore-brighter-documentation/brighter-configuration/inmemoryoptions.md).

The InMemory Inbox provides message deduplication without requiring a database.

## When to Use the InMemory Inbox

**Perfect for**:

* Unit testing duplicate message handling
* Development without database dependencies

**Production Use Cases** (limited):

* Single-process applications
* Short-lived message deduplication windows
* Non-critical deduplication scenarios

## InMemory Inbox Configuration

```csharp
// ...
var bus = new InternalBus();

services.AddConsumers(options =>
{
    options.HandlerLifetime = ServiceLifetime.Scoped;
    options.InboxConfiguration = new InboxConfiguration(
        new InMemoryInbox(TimeProvider.System),
        actionOnExists: OnceOnlyAction.Warn
    );
    options.Subscriptions = subscriptions;
    options.DefaultChannelFactory = new InMemoryChannelFactory(bus, TimeProvider.System);
})
.AutoFromAssemblies();
```

## InMemory Inbox Example Usage

```csharp
// ...
[UseInboxAsync(step: 0, contextKey: typeof(PersonCreatedHandler), onceOnly: true)]
public class PersonCreatedHandler : RequestHandlerAsync<PersonCreated>
{
    private readonly PersonRepository _repository;

    [UseInboxAsync(0, typeof(PersonCreatedHandler), true)]
    public override async Task<PersonCreated> HandleAsync(
        PersonCreated @event,
        CancellationToken cancellationToken = default)
    {
        // Inbox ensures this handler processes each message only once
        var person = await _repository.GetByIdAsync(@event.PersonId);
        person.MarkAsCreated();
        await _repository.SaveAsync(person);

        return await base.HandleAsync(@event, cancellationToken);
    }
}
```

## InMemory Inbox Limitations

* **No persistence**: Deduplication state lost on restart
* **Single process**: Cannot deduplicate across instances
* **Memory bound**: All seen message IDs held in memory
* **No cleanup**: Old entries remain until process restart

## Further Reading

* [InMemory Options for Development and Testing](/paramore-brighter-documentation/brighter-configuration/inmemoryoptions.md) - The full set, and testing patterns


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