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.
- 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.
- Two direct download links for files of format .MBOX:
- https://mail-archives.apache.org/mod_mbox/httpd-announce/202001.mbox
- https://mail-archives.apache.org/mod_mbox/httpd-announce/202002.mbox
- 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:
- 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')
- 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");
// }
}
- 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');
- 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;
// }