SubEtha SMTP

SubEtha SMTP is a Java library designed for receiving SMTP mail with a simple API. Key features include:

• RFC 2821 Compliance: Supports the minimum SMTP specification.
• Security: Supports STARTTLS, SMTP AUTH, and SMTP over SSL/TLS (via server socket factories).
• Developer Experience: Uses builders for a concise and discoverable API.

SubEthaSMTP is a multithreaded server. Each incoming SMTP connection is serviced by a new thread.

Note: You can modify settings related to the number of simultaneous connections on a stopped server, but these settings cannot be changed after start() has been called.

Add the following dependency to your pom.xml to use SubEtha SMTP in your Java project. Replace VERSION_HERE with the desired version.

<dependency>
    <groupId>com.github.davidmoten</groupId>
    <artifactId>subethasmtp</artifactId>
    <version>VERSION_HERE</version>
</dependency>

To use SubEtha SMTP in your Java project, add the following dependency to your pom.xml file. The library is published to the Maven Central Repository, which is active by default in Maven and requires no additional configuration. Ensure you replace VERSION_HERE with the specific version you wish to use (e.g., 7.2.2).

<dependency>
  <groupId>com.github.davidmoten</groupId>
  <artifactId>subethasmtp</artifactId>
  <version>VERSION_HERE</version>
</dependency>

To develop on SubethaSMTP using Eclipse, follow these steps:

1. Clone the repository from GitHub to your local machine.
2. In Eclipse, select Import -> Maven -> Existing Maven Projects.
3. Right-click the POM.XML file and select Run As -> Maven Install to build the project.

SubEthaSMTP requires the SLF4J logging library and JavaMail.

To run the server, you must include:

1. slf4j-api-X.X.X.jar
2. An SLF4J binding jar (e.g., slf4j-simple-X.X.X.jar).

Other bindings like Log4J or java.util.logging can be used if available in the SLF4J distribution.

SubethaSMTP uses the SLF4J logging framework. By default, if no compatible logging connector is found in the classpath, the program will print a warning and discard all log messages. To enable logging, you must include a compatible SLF4J connector in your classpath. The Simple connector is a lightweight option that outputs log messages to stderr.

Note: The version of the connector must match the version that SubethaSMTP was built against.

To run a demonstration SMTP server, download the latest jar-with-dependencies.jar from the GitHub releases section. Execute the BasicSMTPServer example class using the java -cp command. Once running, you can test the server using TELNET or any SMTP client by connecting to TCP port 25000.

java -cp subethasmtp-j3.1.8-jar-with-dependencies.jar org.subethamail.examples.BasicSMTPServer

To process received emails, use the .messageHandler() method in the SMTPServer builder. The handler provides the context, the sender (from), the recipient (to), and the message content as a byte array (data).

SMTPServer server = SMTPServer //
  .port(PORT) //
  .messageHandler(
    (ctx, from, to, data) -> 
       System.out.println(
           "message from " + from 
           + " to " + to
           + ":\n" + new String(data, StandardCharsets.UTF_8)))
  .build();
  
server.start();

You can start a simple SMTP server on a specific port using the SMTPServer builder. Calling .start() begins the server execution asynchronously.

SMTPServer server = SMTPServer 
  .port(25000) 
  .build();
  
//start server asynchronously
server.start();