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https://github.com/tweedegolf/mailcrab

Email test server for development, written in Rust
https://github.com/tweedegolf/mailcrab

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Email test server for development, written in Rust

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# MailCrab



Email test server for development, written in Rust.



Inspired by [MailHog](https://github.com/mailhog/MailHog) and [MailCatcher](https://mailcatcher.me/).



MailCrab was created as an exercise in Rust, trying out [Axum](https://github.com/tokio-rs/axum) and functional components with [Yew](https://yew.rs/), but most of all because it is really enjoyable to write Rust code.



## TLDR



```sh

docker run --rm -p 1080:1080 -p 1025:1025 marlonb/mailcrab:latest

```



## Features



- Accept-all SMTP server

- Web interface to view and inspect all incoming email

- View formatted mail, download attachments, view headers or the complete raw mail contents

- Single binary

- Runs on all `amd64` and `arm64` platforms using docker

- Just a 7.77 MB docker image



![MailCrab screenshot](https://raw.githubusercontent.com/tweedegolf/mailcrab/main/frontend/img/screen.png)



## Related projects



- [CrabAlert](https://github.com/klr/crabalert) is a macOS status bar application that notifies you of incoming messages in MailCrab



## Technical overview



Both the backend server and the frontend are written in Rust. The backend receives email over an unencrypted connection on a configurable port. All email is stored in memory while the application is running. An API exposes all received email:



- `/api/messages` return all message metadata

- `/api/message/[id]` returns a complete message, given its `id`

- `/api/version` returns version information about the executable

- `/ws` send email metadata to each connected client when a new email is received



The frontend initially performs a call to `/api/messages` to receive all existing email metadata and then subscribes for new messages using the websocket connection. When opening a message, the `/api/message/[id]` endpoint is used to retrieve the complete message body and raw email.



The backend also accepts a few commands over the websocket, to mark a message as opened, to delete a single message or delete all messages.



## Installation and usage



You can run MailCrab using docker. Start MailCrab using the following command:



```sh

docker run --rm -p 1080:1080 -p 1025:1025 marlonb/mailcrab:latest

```



Open a browser and navigate to [http://localhost:1080](http://localhost:1080) to view the web interface.



There are also (single) binary builds available, see https://github.com/tweedegolf/mailcrab/releases



### Ports



The default SMTP port is 1025, the default HTTP port is 1080. You can configure the SMTP and HTTP port using environment variables (`SMTP_PORT` and `HTTP_PORT`), or by exposing them on different ports using docker:



```sh

docker run --rm -p 3000:1080 -p 2525:1025 marlonb/mailcrab:latest

```

  

## Host



You can specify the host address MailCrab will listen on for HTTP request using

the `HTTP_HOST` environment variable. In the docker image the default

address is `0.0.0.0`, when running MailCrab directly using cargo or a binary, the default is `127.0.0.1`.



### TLS



You can enable TLS and authentication by setting the environment variable `ENABLE_TLS_AUTH=true`. MailCrab will generate a key-pair and print the self-signed certificate. Any username/password combination is accepted. For example:



```sh

docker run --rm --env ENABLE_TLS_AUTH=true -p 1080:1080 -p 1025:1025 marlonb/mailcrab:latest

```



It is also possible to provide your own certificate by mounting a key and a certificate to `/app/key.pem` and `/app/cert.pem`:



```sh

docker run --rm --env ENABLE_TLS_AUTH=true -v key.pem:/app/key.pem:ro -v cert.pem:/app/cert.pem:ro -p 1080:1080 -p 1025:1025 marlonb/mailcrab:latest

```



### Path prefix



You can configure a prefix path for the web interface by setting and environment variable named `MAILCRAB_PREFIX`, for example:



```sh

docker run --rm --env MAILCRAB_PREFIX=emails -p 1080:1080 -p 1025:1025 marlonb/mailcrab:latest

```



The web interface will also be served at [http://localhost:1080/emails/](http://localhost:1080/emails/)



### Reverse proxy



See [the reverse proxy guide](./reverse_proxy.md).



### Retention period



By default messages will be stored in memory until MailCrab is restarted. This might cause an OOM when MailCrab lives

long enough and receives enough messages.



By setting `MAILCRAB_RETENTION_PERIOD` to a number of seconds, messages older than the provided duration will

be cleared.



### Performance



MailCrab is fast, although there is a bottleneck in the throughput of the websocket connection

(between the server and the browser). If there are many messages sent at once (more than 100 per second)

a client can lag behind and messages can get lost. When dealing with many messages at once,

increasing the internal queue size can help to prevent losing messages.

Use the `QUEUE_CAPACITY` environment variable to set the queue size. De default

is 32, which means that MailCrab can handle 32 messages if the are all sent at the same time.



### docker compose



Usage in a `docker-compose.yml` file:



```yml

version: '3.8'

services:

  mailcrab:

    image: marlonb/mailcrab:latest

    #        environment:

    #            ENABLE_TLS_AUTH: true # optionally enable TLS for the SMTP server

    #            MAILCRAB_PREFIX: emails # optionally prefix the webinterface with a path

    #        volumes:

    #           key.pem:/app/key.pem:ro # optionally provide your own keypair for TLS, else a pair will be generated

    #           cert.pem:/app/cert.pem:ro

    ports:

      - '1080:1080'

      - '1025:1025'

    networks: [default]

```



## Kubernetes deployment



To deploy MailCrab to a Kubernetes cluster, you can use [Helm Chart](./charts/mailcrab/) by cloning this repository and running:



```sh

helm install mailcrab ./charts/mailcrab -f values.yaml

```



For more information on configuring the Helm Chart, see the chart [README](./charts/mailcrab/README.md).



## Sample messages



The `samples` directory contains a couple of test messages. These can be sent using by running:



```sh

cd backend/

cargo test send_sample_messages -- --ignored

```



Alternatively you can send messages using curl:



```sh

curl smtp://127.0.0.1:1025 --mail-from [email protected] --mail-rcpt [email protected] --upload-file samples/normal.email --user 'user:pass'

# with tls

curl -k --ssl-reqd smtps://127.0.0.1:1025 --mail-from [email protected] --mail-rcpt [email protected] --upload-file samples/normal.email --user 'user:pass'

```



## Development



Install [Rust](https://www.rust-lang.org/learn/get-started) and [Trunk](https://trunkrs.dev/)



```sh

# Add wasm as target if it it not present after following the install instructions for Trunk

rustup target add wasm32-unknown-unknown



# clone the code

git clone [email protected]:tweedegolf/mailcrab.git



# start the backend

cd backend

cargo run



# serve the frontend (in a new terminal window)

cd ../frontend

trunk serve



# optionally send test messages in an interval

cd ../backend

cargo test

```