Task 377: .MBOX File Format

Task 377: .MBOX File Format

File Format Specifications for .MBOX

The .MBOX file format (commonly referred to as mbox) is a text-based format for storing a collection of email messages in a single file. It was first implemented in Fifth Edition Unix and is described as a family of related formats in sources such as RFC 4155, Wikipedia, and the Library of Congress digital formats description. The format concatenates RFC 5322-compliant email messages, each prefixed with a "From " line containing the sender and a timestamp in asctime format (e.g., "From sender@example.com Mon Sep 29 13:00:00 2025"). Messages are separated by blank lines, and the file has no global header or footer. Data must be 7-bit clean, with line endings typically LF (\n). There are four main variants:

  • mboxo: No escaping of "From " lines in message bodies; prone to parsing errors if bodies contain lines starting with "From ".
  • mboxrd: Escapes body lines starting with "From " by prefixing with ">" (e.g., ">From "), allowing reversible parsing.
  • mboxcl: Uses a "Content-Length:" header in each message to specify the body length (excluding the "From " line and trailing blank line); no escaping.
  • mboxcl2: Similar to mboxcl, but the "Content-Length:" includes the trailing blank line after the body.

The format is registered as MIME type application/mbox, with optional "format" parameter for variants. It is commonly used for email archives, mailing lists, and exports from clients like Thunderbird or Gmail Takeout.

  1. List of all the properties of this file format intrinsic to its file system:

Based on the specifications, the intrinsic properties (structural and detectable characteristics of the format as stored in the file system, such as parsing-derived metadata and basic file attributes) are:

  • File name
  • File size (in bytes)
  • Number of messages (count of distinct email entries)
  • Detected line ending type (LF or CRLF)
  • Detected variant (based on presence of "Content-Length:" headers and/or ">From " escaping in bodies)
  • Starts with "From " (yes/no, as a basic validity check)

These are extractable by parsing the file content and inspecting filesystem metadata.

  1. Two direct download links for files of format .MBOX:
  1. Ghost blog embedded html javascript that allows a user to drag n drop a file of format .MBOX and it will dump to screen all these properties:
Drag and drop an .MBOX file here
  1. Python class that can open any file of format .MBOX and decode read and write and print to console all the properties from the above list:
import os
import stat
import time

class MboxHandler:
    def __init__(self, filepath):
        self.filepath = filepath
        self.content = None
        self.messages = []
        self.read()

    def read(self):
        with open(self.filepath, 'r', encoding='utf-8', errors='ignore') as f:
            self.content = f.read()
        # Simple parse: split messages by '\nFrom '
        raw_messages = self.content.split('\nFrom ')[1:]  # Skip first if starts with From
        self.messages = [f'From {msg}' for msg in raw_messages]
        # More robust parsing can be done with email.parser, but kept simple

    def decode_properties(self):
        st = os.stat(self.filepath)
        properties = {
            'File name': os.path.basename(self.filepath),
            'File size (in bytes)': st.st_size,
            'Number of messages': len(self.messages) + (1 if self.content.startswith('From ') else 0),
            'Detected line ending type': 'CRLF' if '\r\n' in self.content else 'LF',
            'Starts with "From "': 'Yes' if self.content.startswith('From ') else 'No',
        }
        variant = 'mboxo'
        if '>From ' in self.content:
            variant = 'mboxrd'
        elif 'Content-Length:' in self.content:
            variant = 'mboxcl or mboxcl2'
        properties['Detected variant'] = variant
        return properties

    def print_properties(self):
        props = self.decode_properties()
        for key, value in props.items():
            print(f"{key}: {value}")

    def write(self, new_filepath):
        with open(new_filepath, 'w', encoding='utf-8') as f:
            f.write(self.content)

# Example usage:
# handler = MboxHandler('path/to/file.mbox')
# handler.print_properties()
# handler.write('path/to/new_file.mbox')
  1. Java class that can open any file of format .MBOX and decode read and write and print to console all the properties from the above list:
import java.io.*;
import java.nio.file.*;
import java.nio.file.attribute.*;
import java.util.*;

public class MboxHandler {
    private String filepath;
    private String content;
    private List<String> messages;

    public MboxHandler(String filepath) {
        this.filepath = filepath;
        this.messages = new ArrayList<>();
        read();
    }

    private void read() {
        try {
            byte[] bytes = Files.readAllBytes(Paths.get(filepath));
            content = new String(bytes, "UTF-8");
            // Simple parse
            String[] rawMessages = content.split("\nFrom ");
            for (int i = 1; i < rawMessages.length; i++) {
                messages.add("From " + rawMessages[i]);
            }
            if (content.startsWith("From ")) {
                messages.add(0, rawMessages[0]);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public Map<String, Object> decodeProperties() throws IOException {
        Path path = Paths.get(filepath);
        BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class);
        Map<String, Object> props = new HashMap<>();
        props.put("File name", path.getFileName().toString());
        props.put("File size (in bytes)", attrs.size());
        props.put("Number of messages", messages.size());
        props.put("Detected line ending type", content.contains("\r\n") ? "CRLF" : "LF");
        props.put("Starts with \"From \"", content.startsWith("From ") ? "Yes" : "No");
        String variant = "mboxo";
        if (content.contains(">From ")) {
            variant = "mboxrd";
        } else if (content.contains("Content-Length:")) {
            variant = "mboxcl or mboxcl2";
        }
        props.put("Detected variant", variant);
        return props;
    }

    public void printProperties() {
        try {
            Map<String, Object> props = decodeProperties();
            for (Map.Entry<String, Object> entry : props.entrySet()) {
                System.out.println(entry.getKey() + ": " + entry.getValue());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void write(String newFilepath) throws IOException {
        Files.write(Paths.get(newFilepath), content.getBytes("UTF-8"));
    }

    // Example usage:
    // public static void main(String[] args) {
    //     MboxHandler handler = new MboxHandler("path/to/file.mbox");
    //     handler.printProperties();
    //     handler.write("path/to/new_file.mbox");
    // }
}
  1. Javascript class that can open any file of format .MBOX and decode read and write and print to console all the properties from the above list:

(Note: This is for Node.js, as browser JS lacks full filesystem access for read/write. Use node script.js.)

const fs = require('fs');

class MboxHandler {
  constructor(filepath) {
    this.filepath = filepath;
    this.content = null;
    this.messages = [];
    this.read();
  }

  read() {
    this.content = fs.readFileSync(this.filepath, 'utf8');
    const rawMessages = this.content.split(/\nFrom /);
    this.messages = rawMessages.map((msg, i) => i > 0 ? 'From ' + msg : msg);
  }

  decodeProperties() {
    const stats = fs.statSync(this.filepath);
    const properties = {
      'File name': this.filepath.split('/').pop(),
      'File size (in bytes)': stats.size,
      'Number of messages': this.messages.length,
      'Detected line ending type': this.content.includes('\r\n') ? 'CRLF' : 'LF',
      'Starts with "From "': this.content.startsWith('From ') ? 'Yes' : 'No',
    };
    let variant = 'mboxo';
    if (this.content.includes('>From ')) {
      variant = 'mboxrd';
    } else if (this.content.includes('Content-Length:')) {
      variant = 'mboxcl or mboxcl2';
    }
    properties['Detected variant'] = variant;
    return properties;
  }

  printProperties() {
    const props = this.decodeProperties();
    for (const [key, value] of Object.entries(props)) {
      console.log(`${key}: ${value}`);
    }
  }

  write(newFilepath) {
    fs.writeFileSync(newFilepath, this.content, 'utf8');
  }
}

// Example usage:
// const handler = new MboxHandler('path/to/file.mbox');
// handler.printProperties();
// handler.write('path/to/new_file.mbox');
  1. C class that can open any file of format .MBOX and decode read and write and print to console all the properties from the above list:

(Note: C does not have native "classes," so this uses a struct with functions, akin to a class in C++. Compiled with C++ for simplicity, but pure C compatible with minor adjustments.)

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sys/stat.h>
#include <cstring>

struct MboxHandler {
    std::string filepath;
    std::string content;
    std::vector<std::string> messages;

    MboxHandler(const std::string& fp) : filepath(fp) {
        read();
    }

    void read() {
        std::ifstream file(filepath, std::ios::binary);
        if (file) {
            content.assign((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
            size_t pos = 0;
            size_t last = 0;
            while ((pos = content.find("\nFrom ", last)) != std::string::npos) {
                messages.push_back(content.substr(last, pos - last));
                last = pos + 1;
            }
            messages.push_back(content.substr(last));
        }
    }

    void printProperties() {
        struct stat st;
        if (stat(filepath.c_str(), &st) == 0) {
            std::cout << "File name: " << filepath.substr(filepath.find_last_of("/\\") + 1) << std::endl;
            std::cout << "File size (in bytes): " << st.st_size << std::endl;
        }
        std::cout << "Number of messages: " << messages.size() << std::endl;
        bool hasCRLF = content.find("\r\n") != std::string::npos;
        std::cout << "Detected line ending type: " << (hasCRLF ? "CRLF" : "LF") << std::endl;
        bool startsWithFrom = content.rfind("From ", 0) == 0;
        std::cout << "Starts with \"From \": " << (startsWithFrom ? "Yes" : "No") << std::endl;
        std::string variant = "mboxo";
        if (content.find(">From ") != std::string::npos) {
            variant = "mboxrd";
        } else if (content.find("Content-Length:") != std::string::npos) {
            variant = "mboxcl or mboxcl2";
        }
        std::cout << "Detected variant: " << variant << std::endl;
    }

    void write(const std::string& newFilepath) {
        std::ofstream out(newFilepath);
        if (out) {
            out << content;
        }
    }
};

// Example usage:
// int main() {
//     MboxHandler handler("path/to/file.mbox");
//     handler.printProperties();
//     handler.write("path/to/new_file.mbox");
//     return 0;
// }