Combine a directory of .eml files into a single Unix "mbox" file.

emlToMbox.py

#!/usr/bin/env python3

""" Converts a directory full of .eml files to a single Unix "mbox" file.
This is similar to http://www.cosmicsoft.net/emlxconvert.html

Accepts as input either an individual .eml file or a directory containing one
or more .eml files.

Usage:
$ ./emlToMbox.py inputdir/ output.mbox
$ ./emlToMbox.py input.eml output.mbox

STATUS:  Lightly tested using Python 3.9.1 
"""

import os
import sys
import mailbox

global debug
debug = True

def main( arguments ):
    infile_name = arguments[1]
    dest_name = arguments[2]
    
    if debug:
        print("Input is:  " + infile_name)
        print("Output is: " + dest_name)
    
    dest_mbox = mailbox.mbox(dest_name, create=True) # if dest doesn't exist create it
    dest_mbox.lock() # lock the mbox file
    
    if os.path.isdir(infile_name):
        if debug:
            print("Detected directory as input, using directory mode")
        count = 0
        for filename in os.listdir(infile_name):
            if filename.split('.')[-1] == "eml":
                try:
                    fi = open(os.path.join(infile_name, filename), 'r')
                except:
                    sys.stderr.write("Error while opening " + filename + "\n")
                    dest_mbox.close()
                    raise
                addFileToMbox( fi, dest_mbox )
                count += 1
                fi.close()
        if debug:
            print("Processed " + str(count) + " total files.")
    
    if infile_name.split('.')[-1] == "eml":
        if debug:
            print("Detected .eml file as input, using single file mode")
        try:
            fi = open(infile_name, 'r')
        except:
            sys.stderr.write("Error while opening " + infile_name + "\n")
            dest_mbox.close()
            raise
        addFileToMbox( fi, dest_mbox )
        fi.close()
    
    dest_mbox.close() # close/unlock the mbox file
    return 0

def addFileToMbox( fi, dest_mbox ):
    # Any additional preprocessing logic goes here...
    try:
        dest_mbox.add( fi )
    except:
        dest_mbox.close()
        raise

if __name__ == "__main__":
    if len(sys.argv) != 3:
        sys.stderr.write("Usage: ./emlToMbox.py input outbox.mbox\n")
        sys.exit(1)
    sys.exit( main( sys.argv ) )

This worked great. Thank you! 🙏