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Overview

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.

Screenshot

FakeSMTP uses SubEtha SMTP: 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.

Requirements

You need Java JVM 11 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.

Usage

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.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.jar -o output_directory_name

You can also start the SMTP server automatically at launch (-s argument) on a different port (-p argument) with no gui (-b argument),
the following example will autostart the SMTP server on the port 2525 and bound to the loopback address (-a argument):

 java -jar fakeSMTP.jar -s -b -p 2525 -a 127.0.0.1

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 the available options (relay domains, custom eml-viewer...), run:

 java -jar fakeSMTP.jar --help

Usage on Docker

  • Run distributed version: Dockerfile 
     docker build -t="mail" github.com/tntim96/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/tntim96/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

Alternatives

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:

  • SMTP4dev
    • Nice features;
    • Open source;
    • Written for Windows in .net.
  • DevNull SMTP
    • Lightweight;
    • Closed source;
    • Written in Java 1.4 (cross platform).