About GreenMail

Introduction

GreenMail is an open source, intuitive and easy-to-use test suite of email servers for testing purposes.

Typical use cases include mail integration testing or lightweight sand boxed mail server for development.

• Supports SMTP, POP3 and IMAP including TLS/SSL
• Prevents accidental email leaking to real mail servers (non-forwarding / sand-boxed)
• Embeds in JUnit test for integration testing
• Provides flexible standalone run options such as
  • standalone JVM process
  • WAR module
  • docker image

Scenarios

GreenMail is useful in the following scenarios:

Test Your Sending Code

• System testing an application. GreenMail responds like a regular SMTP server but does not deliver any email, which enables it to be used in real life applications and real test cases. Messages can easily be extracted, verified and modified. Support for SMTPS (SSL) is enabled.
• GreenMail is an excellent choice for unit testing code that needs to send email with a succinct, efficient (non-polling) way to wait for messages to arrive, retrieve, verify, and modify messages.
• Note that retrieval of emails can be made with a simple java method or through a provided POP3, IMAP retriever helper class. Alternatively you can use a local client like Thunderbird.
• The example below is using the GreenMail JUnit rule. See examples for hints on how to use GreenMail without the rule.

@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetupTest.SMTP);

@Test
public void testSend() throws MessagingException {
    GreenMailUtil.sendTextEmailTest("to@localhost", "from@localhost",
        "some subject", "some body"); // --- Place your sending code here instead
    assertEquals("some body", greenMail.getReceivedMessages()[0].getContent());
}
        

Test Your Retrieving Code

• Again GreenMail can be used for system or unit testing an application needing to use POP3 or IMAP by responding like a standard compliant POP3 or IMAP server. Support for POP3S and IMAPS (SSL) is also enabled.
• Messages can be placed directly in users mailboxes, by using SMTP or preloaded from file system.
• GreenMail ships with helper classes for sending and retrieving. See the javadocs for the Retriever.java class

@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetupTest.SMTP_IMAP);

@Test
public void testReceive() throws MessagingException {
    GreenMailUser user = greenMail.setUser("to@localhost", "login-id", "password");
    user.deliver(createMimeMessage()); // You can either create a more complex message...
    GreenMailUtil.sendTextEmailTest("to@localhost", "from@localhost",
        "subject", "body"); // ...or use the default messages

    assertEquals(2, greenMail.getReceivedMessages().length); // // --- Place your POP3 or IMAP retrieve code here
}
        

Sending and Retrieving

GreenMail can easily be configured to use all or a combination of ports, protocols, and bind addresses. For example, it's possible to run GreenMail on SMTP, POP3, POP3S and IMAPS ports as easily as only SMTP. Many systems might already be running these servers or don't allow non-root users to open the default ports which is why GreenMail ships with a special configuration for testing.

Mocking a mail server for your development environment

GreenMail provides a JBoss GreenMail service for mocking a mail server for development. It saves you the overhead of either installing a full productive server (like Apache James).

Check out the possible deployments as webapp, standalone or standalone docker image.

Implementation

The implementation is in 100% Java with only a few library dependencies for GreenMail Core:

• Jakarta Mail
• Java Activation Framework
• SLF4J Simple Logging Facade for Java for logging
• Junit - required for easy test setup using Rules

GreenMail contains several modules:

• com.icegreen:greenmail-core - Core library for unit tests
• com.icegreen:greenmail-standalone - Standalone runner (e.g. when not using GreenMail embedded into unit test)
• com.icegreen:greenmail-docker-standalone - Dockerized standalone runner
• com.icegreen:greenmail-junit4 - JUnit4 support via GreenMailRule
• com.icegreen:greenmail-junit5 - JUnit5 support via GreenMailExtension
• com.icegreen:greenmail-webapp
• com.icegreen:greenmail-spring - Spring framework support via GreenMailBean

Source Code

You find the source on GitHub including build instructions. GreenMail is open source released under The Apache 2.0 License.

GreenMail's protocol source code is based on a cocktail of Foedus and James.

Links

The following lists provide helpful links related to GreenMail and email integration testing.

Projects extending/wrapping GreenMail:

• Example container integrations of GreenMail and various web based mail clients
• Citrus Integration Testing used GreenMail for mocking mail server
• Spring Integration 5.5 uses now GreenMail for email integration testing
• GreenMail HTTP encapsulates GreenMail Standalone, adds a web server to deliver JSON and web pages showing the internals of GreenMail
• Grails Plugin for GreenMail including REST-like GreenMail control interface and UI
• Play Plugin for GreenMail including REST-like control interface and UI
• JCA Adapter for GreenMail
• Deprecated SourceForge GreenMail project location before migration to GitHub in 2014

Articles&Blogs:

• Manually testing email notifications with GreenMail mock mail server
• "Testing email with GreenMail, a mock mail server" @ OpenValue Meetup
• Use GreenMail For Spring Mail (JavaMailSender) JUnit 5 Integration Tests
• Spring Boot Admin and GreenMail
• Deploy local email server mock for testing with GreenMail
• Catch-all SMTP servers for development and testing
• Using GreenMail to enhance JHipster integration tests
• Using dynamic ports in spring boot integration tests
• Integration Testing IMAP, SMTP and POP3 with GreenMail
• Unit testing Java mail code

Projects using GreenMail include:

• Spring Integration 5.5 uses now GreenMail
• Alfresco
• Salesforce MuleSoft
• ... and many more. Tell us about your project :-)

Related projects to JavaMail and testing/development:

• Wiser alias Subethasmtp,
• Apache James, a full-blown enterprise mail server
• DevNullSmtp
• JavaMail Mock2
• Collection of IMAP related RFCs

Thanks

Special thanks to all contributors for feedback and patches!

Many thanks to and JetBrains for supporting this project with free OSS licenses!

Examples

Using JUnit4 rule based setup

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleRuleTest.java) */
@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetupTest.SMTP);

@Test
public void testSomething() {
    GreenMailUtil.sendTextEmailTest("to@localhost", "from@localhost", "subject", "body");
    MimeMessage[] emails = greenMail.getReceivedMessages();
    assertEquals(1, emails.length);
    assertEquals("subject", emails[0].getSubject());
    assertEquals("body", emails[0].getContent());
    // ...
}
        

Using JUnit5 extension

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-junit5/src/test/java/com/icegreen/greenmail/junit5/CustomSetupTests.java) */
@RegisterExtension
static GreenMailExtension greenMail = new GreenMailExtension(ServerSetupTest.SMTP);

@Test
@DisplayName("Send test")
void testSend() {
    GreenMailUtil.sendTextEmailTest("to@localhost", "from@localhost", "some subject", "some body");
    final MimeMessage[] receivedMessages = greenMail.getReceivedMessages();
    final MimeMessage receivedMessage = receivedMessages[0];
    assertEquals("some body", receivedMessage.getContent());
}
        

Testing your sending code (simple)

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleSendTest.java) */
GreenMail greenMail = new GreenMail(); //uses test ports by default
greenMail.start();
GreenMailUtil.sendTextEmailTest("to@localhost", "from@localhost", "some subject",
                                "some body"); // --- Place your sending code here
assertEquals("some body", greenMail.getReceivedMessages()[0].getContent());
greenMail.stop();
        

Testing your sending code (detecting available port)

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleSendTest.java) */
GreenMail greenMailWithDynamicPort = new GreenMail(ServerSetupTest.SMTP.dynamicPort()); // Try to find available port
greenMailWithDynamicPort.start();
try {
    GreenMailUtil.sendTextEmail(
        "to@localhost", "from@localhost", "some subject", "Sent using available port detection",
        greenMailWithDynamicPort.getSmtp().getServerSetup()); // Important: Pass dynamic port setup here
    assertEquals("Sent using available port detection", greenMailWithDynamicPort.getReceivedMessages()[0].getContent());
    assertNotEquals("Dynamic port must differ", ServerSetupTest.SMTP.getPort(), greenMailWithDynamicPort.getSmtp().getPort());
} finally {
    greenMailWithDynamicPort.stop();
}
        

Testing your sending code (advanced)

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleSendNoRuleAdvTest.java) */
GreenMail greenMail = new GreenMail(ServerSetupTest.ALL);
greenMail.start();

//Use random content to avoid potential residual lingering problems
final String subject = GreenMailUtil.random();
final String body = GreenMailUtil.random();

sendTestMails(subject, body); // --- Place your sending code here

//wait for max 5s for 1 email to arrive
//waitForIncomingEmail() is useful if you're sending stuff asynchronously in a separate thread
assertTrue(greenMail.waitForIncomingEmail(5000, 2));

//Retrieve using GreenMail API
Message[] messages = greenMail.getReceivedMessages();
assertEquals(2, messages.length);

// Simple message
assertEquals(subject, messages[0].getSubject());
assertEquals(body, messages[0].getContent());

//if you send content as a 2 part multipart...
assertTrue(messages[1].getContent() instanceof MimeMultipart);
MimeMultipart mp = (MimeMultipart) messages[1].getContent();
assertEquals(2, mp.getCount());
assertEquals("body1", mp.getBodyPart(0).getContent());
assertEquals("body2", mp.getBodyPart(1).getContent());

greenMail.stop();
        

Testing your retrieving code

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleReceiveTest.java) */
//Start all email servers using non-default ports.
GreenMail greenMail = new GreenMail(ServerSetupTest.ALL);
greenMail.start();

//Use random content to avoid potential residual lingering problems
final String subject = GreenMailUtil.random();
final String body = GreenMailUtil.random();
MimeMessage message = createMimeMessage(subject, body, greenMail); // Construct message
GreenMailUser user = greenMail.setUser("wael@localhost", "waelc", "soooosecret");
user.deliver(message);
assertEquals(1, greenMail.getReceivedMessages().length);

// --- Place your retrieve code here
greenMail.stop();
        

Testing using plain JavaMail for sending/retrieving code

/** [See code on GitHub](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-core/src/test/java/com/icegreen/greenmail/examples/ExampleJavaMailTest.java) */
@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetupTest.SMTP_IMAP);

@Test
public void testSendAndReceive() throws MessagingException, ... {
    Session smtpSession = greenMail.getSmtp().createSession();

    Message msg = new MimeMessage(smtpSession);
    msg.setFrom(new InternetAddress("foo@example.com"));
    msg.addRecipient(Message.RecipientType.TO,
            new InternetAddress("bar@example.com"));
    msg.setSubject("Email sent to GreenMail via plain JavaMail");
    msg.setText("Fetch me via IMAP");
    Transport.send(msg);

    // Create user, as connect verifies pwd
    greenMail.setUser("bar@example.com", "bar@example.com", "secret-pwd");

    // Alternative 1: Create session and store or ...
    Session imapSession = greenMail.getImap().createSession();
    Store store = imapSession.getStore("imap");
    store.connect("bar@example.com", "secret-pwd");
    Folder inbox = store.getFolder("INBOX");
    inbox.open(Folder.READ_ONLY);
    Message msgReceived = inbox.getMessage(1);
    assertEquals(msg.getSubject(), msgReceived.getSubject());
    ...

    // Alternative 2: ... let GreenMail create and configure a store:
    IMAPStore imapStore = greenMail.getImap().createStore();
    imapStore.connect("bar@example.com", "secret-pwd");
    inbox = imapStore.getFolder("INBOX");
    inbox.open(Folder.READ_ONLY);
    msgReceived = inbox.getMessage(1);
    ...

    // Alternative 3: ... directly fetch sent message using GreenMail API
    assertEquals(1, greenMail.getReceivedMessagesForDomain("bar@example.com").length);
    msgReceived = greenMail.getReceivedMessagesForDomain("bar@example.com")[0];
    ...
}
        

Testing using Spring framework

/** See [GreenMailBeanTest.java](https://github.com/greenmail-mail-test/greenmail/tree/master/greenmail-spring/src/test/java/com/icegreen/greenmail/spring/GreenMailBeanTest.java)
 * and [GreenMailBeanTest-context.xml](greenmail-spring/src/test/resources/com/icegreen/greenmail/spring/GreenMailBeanTest-context.xml)
*/
@Autowired
private GreenMailBean greenMailBean;

@Test
public void testCreate() {
    GreenMail greenMail = greenMailBean.getGreenMail();
    ...
}
        

Deployment

Run GreenMail as standalone java application

Running GreenMail as a standalone process is useful if you want a simple sand boxed mail server.

All you require is a compatible JRE and the standalone JAR. The standalone JAR already contains all dependencies and a default logging.

You can configure GreenMail by setting system properties, and activate a minimal RESTful API (requires GreenMail 1.6.2+) for e.g. adding users, purging mails or resetting GreenMail instance.

Starting GreenMail standalone

java [OPTIONS] -jar greenmail-standalone.jar
                

tmp
  └──preload-example
       ├── bar@localhost       # Creates user (login and credentials default to email)
       │   └── INBOX
       │       └── test-5.eml  # Loads email
       ├── drafts@localhost
       │   └── Drafts          # Creates folder
       ├── foo-bar@localhost
       └── foo@localhost
           ├── Drafts
           │   └── draft.eml
           └── INBOX
               ├── f1
               │   ├── f2
               │   │   ├── test-3.eml
               │   │   └── test-4.eml
               │   └── test-2.eml
               └── test-1.eml
                                

GreenMail standalone examples

Test setup for SMTP/IMAP and one user

java -Dgreenmail.setup.test.smtp -Dgreenmail.setup.test.imap \
     -Dgreenmail.users=test1:pwd1 -jar greenmail-standalone.jar
                

Test setup for SMTP(S)/IMAP(S)/POP3(S) and two user

java -Dgreenmail.setup.test.all -Dgreenmail.users=test1:pwd1,test2:pwd2@example.com \
     -jar greenmail-standalone.jar
                

Test setup for SMTP(S)/IMAP(S)/POP3(S), one user and bound to 0.0.0.0

java -Dgreenmail.setup.test.all -Dgreenmail.users=test1:pwd1 \
     -Dgreenmail.hostname=0.0.0.0 \
     -jar greenmail-standalone.jar
                

SMTP only

java -Dgreenmail.smtp.hostname=127.0.0.1 -Dgreenmail.smtp.port=4025 \
     -jar greenmail-standalone.jar
                

Deploy as a standalone Docker image

GreenMail provides a pre-configured Docker image running GreenMail standalone. The image is available via Docker Hub Public Repository, but you can also build it yourself using our Dockerfile.

By default, GreenMail standalone runs as user greenmail using the GreenMail test setup with the following default settings and exposed ports.

Using docker to run the image

docker pull greenmail/standalone:2.0.1
docker run -t -i -p 3025:3025 -p 3110:3110 -p 3143:3143 \
                 -p 3465:3465 -p 3993:3993 -p 3995:3995 -p 8080:8080 \
                 greenmail/standalone:2.0.1
                

If you want to test it, you can do a quick check with telnet (or any other mail program) by connecting to the exposed SMTP port and checking if GreenMail SMTP server responds:

Passing configuration options to GreenMail Standalone Docker image

You can also configure the JVM and GreenMail configuration options via the Docker environment variables JAVA_OPTS and GREENMAIL_OPTS:

docker run -t -i \
           -e GREENMAIL_OPTS='-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.auth.disabled -Dgreenmail.verbose' \
           -e JAVA_OPTS='-Djava.net.preferIPv4Stack=true -Xmx512m' \
           -p 3025:3025 -p 3110:3110 -p 3143:3143 \
           -p 3465:3465 -p 3993:3993 -p 3995:3995 -p 8080:8080 \
           greenmail/standalone:2.0.1
                

Deploy as a webapp (WAR)

GreenMail Webapp provides a lightweight Java web application wrapping GreenMail mail server and exposing GreenMail API.

The usage scenario is a development or test environment where a real mail server is too much overhead. The webapp is application server neutral - you should be able to use it on any Java EE 7 application server (Servlet 3.1) running and Java 8 (or greater).

With the GreenMail mail service each developer has its own local mail server sandbox - so there's no danger for accidentally leaking test mails into the Internet.

Deploy the webapp

Simply deploy the webapp like any other Java web application.

For Tomcat, just drop the webapp into $CATALINA_HOME/webapps directory. Alternatively, you can create a $CATALINA_HOME/webapps/greenmail, unpack the WAR here and configure the GreenMail service.

Configure the webapp

You can configure the active mail services and available users by editing WEB-INF/web.xml in the WAR file and modifying the context params. A ServletContextListener starts and stops the GreenMail service when deploying/un-deploying.

Have a look at the default web.xml.

Features

API

GreenMail provides a RESTful API focusing on administrative tasks like purging mails or adding users.

Operations include

• Getting currently configured user and adding new users
• Getting current configuration (e.g. which service like SMTP runs on which port)
• Purging all mailboxes of emails
• Resetting GreenMail to original configuration (restarts server, purges all mails and users added via API)
• Getting mail messages for a user and optional folder (simplified, containing message uid/subject/raw mime message as recommended usage is via e.g. IMAP)

The OpenAPI rendered UI can be used for invoking the API, e.g. for adding a new user:

Preloading emails from filesysem

You can preload user/folder/emails from filesystem

Delivery Status Notification (DSN)

You can provide custom DSN behavior by implementing MessageDeliveryHandler.java. See ExampleUndeliverableTest.java

FAQ

How come I don't have to create any accounts to send/retrieve?

By default, GreenMail accepts all incoming emails. If there is no corresponding existing email account, one is automatically created with login and password being the same as the to-address.

What other library dependencies are there?

Check out the Maven POM. Dependencies include

• javamail.jar and activation.jar
• slf4j-api.jar (for logging)
• junit.jar (for test rules)

How come I don't need to install any SSL/TLS related certificates?

GreenMail is designed to be used out of the box with no need to generate, sign or install any certificates into your keystore. GreenMail ships with a builtin keystore with a self-signed RSA key. Refer to the source code of DummySSLServerSocketFactory for details.

How can I replace the included default certificate?

You can use the system properties -Dgreenmail.tls.keystore.file and -Dgreenmail.tls.keystore.password for pointing to your own PKCS12 file and password, if you do not want to use the provided default one (included in GreenMail JAR).

How can I use IMAP quotas?

GreenMail supports IMAP quota. Quota capability can be toggled on and off. For details see ImapServerTest.java quota test

How can I create or delete a mail user?

GreenMail greenMail = ...
// Create user with login id equals email
GreenMailUser user1 = greenMail.setUser("foo@localhost", "some secret pwd");
// Create user with login id different than email
GreenMailUser user2 = greenMail.setUser("foo@localhost", "login-id", "some secret pwd");
...
greenMail.getManagers().getUserManager().deleteUser(user1); // Delete user

How can I get more verbose output?

Enable the verbose mode, which prints debug output and protocol level communication.
See ServerSetup.setVerbose(boolean) or GreenMail standalone runner option greenmail.verbose option.

Example of activating verbose mode when configuring via GreenMailRule:

@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetup.verbose(ServerSetupTest.SMTP_IMAP));

How can I let GreenMail dynamically choose available port?

Set the port to 0 or use ServerSetup.SMTP.dynamicPort(), and GreenMail will try to find an available port.

@Rule
public final GreenMailRule greenMail = new GreenMailRule(ServerSetup.SMTP.dynamicPort());

GreenMailUtil.sendTextEmail("to@localhost", "from@localhost", "subject", "body",
    greenMail.getSmtp().getServerSetup());

How can I preload an existing (eml) message?

You can load an existing electronic mail (eml) message and store the message for a user in a mailbox folder.

Example: ExamplePreloadMailFromFsTest.java

How can I use nested test classes (with @Nested)?

When specifying .withPerMethodLifecycle(false), greenmail will initialize as "before all" for every test class. When using nested test classes this leads to an initialization in the main test class and in every nested test class. This in turn leads to the following error: "Address already in use: bind".

To circumvent that you need to override the before all behaviour and suppress the initialization in nested test classes.

public class NestedTest {
    @RegisterExtension
    protected static GreenMailExtension greenMail = new GreenMailExtension(ServerSetupTest.SMTP) {
        @Override
        public void beforeAll(ExtensionContext context) {
            if (context.getTestClass().isPresent()) {
                Class currentClass = context.getTestClass().get();
                if (!ModifierSupport.isStatic(currentClass) && currentClass.isMemberClass()) {
                    return;
                }
            }
            super.beforeAll(context);
        }
    }
        .withConfiguration(
            GreenMailConfiguration.aConfig().withUser("user", "pw"))
        .withPerMethodLifecycle(false);

    @Nested
    class NestedTestClass {
        @Test
        public void testA() {
            // test something
        }
    }
}

How can I configure mail session properties?

You can configure per protocol specific mail session properties:

GreenMail greenMail = new GreenMail(new ServerSetup[]{
        ServerSetupTest.SMTP,
        ServerSetupTest.IMAP.mailSessionProperty("mail.imap.minidletime", "100")
});
Session session = greenMail.getImap().createSession(); // Will have configured property set

How can I direcly (avoiding IMAP/POP3) search received messages in my tests?

GreenMail provides direct access to internal user mailboxes and received messages:

// All messages received for emails ending with "localhost" and subject containing "match"
final List messages = greenMail.findReceivedMessages(
        u -> u.getEmail().toLowerCase().endsWith("localhost")      /* Predicate for user account, selecting users by email ending with 'localhost' */,
        m -> MimeMessageHelper.getSubject(m, "").contains("match") /* Predicate for messages, selecting messages with subject attribute containing "match"*/
    ).collect(Collectors.toList());

Requires 2.1.0+

Download

Maven Central contains all GreenMail artifacts.

Docker images are available on Docker Hub GreenMail Repository, such as for the GreenMail standalone runner.

Quick-links

• GreenMail 2.1.x downloads (for Jakarta Mail 2.1)
• GreenMail 2.0.x downloads (for Jakarta Mail 2.0)
• GreenMail 1.6.x downloads (for Jakarta Mail 1.6)

Please note that the downloads are sorted by version and not by release date. GitHub releases page shows the releases cronological sorted.

2.1.3 - February 4th, 2025

Available via Maven repository or as a ZIP from GitHub.

2.0.1 - Nov 17th, 2023

Available via Maven repository or as a ZIP from GitHub.

1.6.15 - December 3rd, 2023

Available via Maven repository or as a ZIP from GitHub.

1.5.14 - July 4th, 2020

Available via Maven repository or as a ZIP from GitHub.

1.5.11 - Oct 22, 2019

Available via Maven repository or as a ZIP from GitHub.

1.4.1 - April 27th, 2015

Download bundle as ZIP from GitHub.

1.3.1b - June 14th 2009

Older versions

You can find older version at the old SourceForge download section