Dummy SMTP server with GUI for testing emails in applications easily.
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FakeSMTP is a Free Fake SMTP Server with GUI for testing emails in applications easily. It is written in Java.

Configure your application to use localhost as your SMTP server, and all emails will be intercepted and displayed in this software.

FakeSMTP uses SubEthaSMTP: an easy-to-use server-side SMTP library for Java.

FakeSMTP is free to use for commercial and non-commercial projects and the source code is provided.

It is licensed under the very free BSD or GPL license, whichever you prefer.


You need Java JVM 1.6 or newer installed on your machine.

If you are on a "Unix-like" machine (Mac, GNU/Linux, BSD...), you may have to be "root" to start the port 25, otherwise, try another port >= 1024.


The fakeSMTP.jar is auto-executable. If your desktop environment supports it, you can directly double click on the .jar file. Otherwise, run the following command:

java -jar fakeSMTP-VERSION.jar

If you want to specify the directory where emails will be saved when starting the application, you can use the -o argument:

java -jar fakeSMTP-VERSION.jar -o output_directory_name
java -jar fakeSMTP-VERSION.jar --output-dir output_directory_name

If you want to autostart the SMTP server at launch, you can use the -s argument:

java -jar fakeSMTP-VERSION.jar -s
java -jar fakeSMTP-VERSION.jar --start-server

If you want to autostart the SMTP server without a GUI (background) on a different port and bound to the loopback address:

java -jar fakeSMTP-VERSION.jar -s -b -p 2525 -a
java -jar fakeSMTP-VERSION.jar --start-server --background --port 2525 --bind-address

If you don't need to save emails on the filesystem (to improve the overall performances), you can use the -m (memory mode) argument:

java -jar fakeSMTP-VERSION.jar -m

To see all the available options (relay domains, custom eml-viewer...):

java -jar fakeSMTP-VERSION.jar --help


FakeSMTP was created because we couldn't find any free (as in freedom) and cross-platform SMTP server with GUI for testing emails in applications or websites. Listed below are some greats alternatives to Fake SMTP:


  • Nice features;
  • Open source;
  • Windows only (written in .Net).

DevNull SMTP

  • Lightweight;
  • Closed source;
  • Cross-Platform (written in Java 1.4).

Building it

You need to download and setup Maven. Once installed, go to project directory and run the following command:

mvn package -Dmaven.test.skip

This command will create an executable jar on the target folder.

We recommend you not to skip unit tests.

Once you know how to configure unit tests for this project, stop skipping them.

Running integration tests

To run integration tests, you will first need to launch the application and start the server on port 2525.

java -jar fakeSMTP-VERSION.jar -p 2525 -s

You can then run the following command:

mvn integration-test

Change the default port for unit/integration tests

You need to modify the following file: src/test/java/com/nilhcem/fakesmtp/core/test/TestConfig.java.

Please note that it is better to have two different ports for unit and integrations tests, to avoid any port binding exception while running Maven's integration-test goal.

Usage on Docker

  • Run distributed version: Dockerfile

    `docker build -t="mail" github.com/Nilhcem/FakeSMTP`
    `docker run -ti -p 250:25 --privileged=true -v /mail:/output mail`
  • Build from source

Get sources from GitHub: Dockerfile

git clone https://github.com/Nilhcem/FakeSMTP
cd FakeSMTP

Build the docker image

mvn package docker:build -DskipTests

Run the docker image

docker run -ti -d fakesmtp

Configure container

  • Map the SMTP port 25 to host:

    -p 250:25

  • Map volume for received mails:

    --privileged=true -v /mail-data:/output

Full command

  • Foward fakesmtp:25 to host port 250,

  • mount host folder /home/fakesmtp/mail as container folder /output

    docker run -ti -d -p 250:25 --privileged=true -v /home/fakesmtp/mail:/output fakesmtp

Contact me

Use my github's nickname (at) gmail (dot) com