Create MBOX Files in Java

For Java developers who want to equip their email applications with the ability to work with storage files, Aspose.Email for Java offers an efficient API that simplifies the process of creating storage files and manipulating them while maintaining high performance and reliability. In this article, we will learn about a popular MBOX storage file format and the Java API that we’re going to use to create MBOX files, add EML files to them and open them in Thunderbird. You will be able to explore and test practical code samples to get started.

What is Mbox File Format?

MBOX format is commonly used for storing email messages in a single file. It consists of a plain text file that contains a series of email messages concatenated together, with each message separated by a “From” line followed by the sender’s email address. This structure allows for efficient storage and retrieval of emails. Each message within the file includes headers (such as “From:”, “To:”, “Subject:”, etc.) followed by the message body. MBOX files can contain email messages with attachments. Attachments are encoded within the message body using methods like MIME (Multipurpose Internet Mail Extensions), making it possible to extract and decode attachments programmatically. MBOX files are versatile and can be opened by various email clients, making them a popular choice for archiving and exporting email messages.

Java API to Work with Files in Mbox Format

Working with MBOX files is a common requirement in email applications, especially for archiving and exporting purposes. Aspose.Email for Java simplifies this process with its intuitive components and straightforward approach. It is a feature-rich Java library designed to handle various email-related tasks, including message manipulation in different formats, attachment management, and email conversion. With its intuitive design and comprehensive functionality, Aspose.Email empowers Java developers to build sophisticated email applications with ease. To leverage the power of the API, refer to its download page or directly to Maven repository. The users are provided with a demo version and installation instructions.

Creating MBOX Files

With Aspose.Email for Java, create an MBOX file in just two lines of code. For this purpose, we’re going to use the MboxrdStorageWriter class which also provides methods for writing messages and managing the MBOX file structure. For detailed information about the class, including its constructors, methods, and usage examples, you can refer to the Aspose.Email for Java documentation or API reference. Additionally, if you have the library added to your project, you can explore the class directly within your IDE’s documentation view or by hovering over the class name in your code. The following code sample demonstrates how to create an MBOX file with the Aspose.Email writer in Java:

  1. Begin by specifying the location and name of the MBOX file you intend to create. This is done by defining a file path, for example, “output.mbox”.
  2. Then, initialize an instance of MboxrdStorageWriter with the specified output file. This writer class allows you to write messages to the MBOX file.

With this setup, you’re ready to start adding messages to the MBOX file using the writer instance.

Import EML Files to a MBOX File

Import an EML file into an MBOX file using Aspose.Email for Java seamlessly following a few key steps. Load an existing EML file with the load method of the MailMessage class, then add it to the created storage using the writeMessage method of the MboxrdStorageWriter class. The following code sample demonstrates how to add a message to a storage file:

  1. Specify the path of the EML file you want to import.
  2. Specify the path and the name of the MBOX file to be created.
  3. Load the EML file using the MailMessage.load() method, which converts the EML content into a MailMessage object.
  4. Create an instance of MboxrdStorageWriter responsible for writing messages to the MBOX file.
  5. Use the writeMessage() method of the MboxrdStorageWriter instance to write the loaded EML message to the MBOX file.

Open MBOX Files in Thunderbird

The user-friendly interface of Thunderbird makes it easy to view and organize emails from MBOX files, providing a seamless solution for accessing archived email data. By following a few simple steps, you can seamlessly import MBOX files into Thunderbird and browse through the emails contained in them. This process provides a convenient way to manage and read email data stored in MBOX format within the familiar interface of Thunderbird.

Once you have the MBOX file ready, you can follow these steps to open it in Thunderbird:

  1. Launch Thunderbird on your computer.
  2. Click on the “Menu” button (three horizontal lines) located at the top right corner of the Thunderbird window.
  3. From the dropdown menu, choose “Tools” and then click on “Import…”
  4. In the Import window, select the option “Import everything from an MBOX file” and click “Next.”
  5. Choose the file you want to open by clicking on the “Select File” button.
  6. Locate and select your file from the file explorer window, and then click on “Open.”
  7. It will be imported by Thunderbird. Click “Finish” to close the Import dialog box when the import process is complete.
  8. The imported file should now be visible in the Thunderbird client, listed as a new folder in the left-hand panel.
  9. You can now click on the imported folder to view its contents in Thunderbird.


In this article, we delved into the widely-used MBOX storage file format and explored how to utilize a robust Java API to create MBOX files, incorporate EML files into them, and seamlessly open them in Thunderbird. For Java developers seeking to enhance their email applications with robust storage capabilities, Aspose.Email for Java stands out as a reliable solution. We provided you with practical code samples and insights into its key components such as the MboxrdStorageWriter class, and ways to start utilizing the library effectively in your projects. With its intuitive design and comprehensive functionality, API streamlines the process of creating and managing storage files, ensuring efficiency, performance, and reliability enhancing productivity and user experience.

Additionally, users can have a free access to:

  • documentation, providing comprehensive guides, tutorials, and examples to assist users in understanding and utilizing the API’s features effectively
  • API reference, a detailed guide to the classes, methods, and properties available in the library
  • support forum, where users can seek assistance, share insights, and collaborate with fellow developers
  • blog, which offers a wealth of articles, tutorials, and announcements, keeping users informed about the latest updates, features, and use cases of the API

All these resources are invaluable for further guidance and insights into the capabilities of the Aspose.Email for Java.

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