OfflineImap to Thunderbird

Sat 08 February 2014

Last week I moved from Debian to Linux Mint and setup Thunderbird as my new mail client(replacing mutt). Sadly for some reason Thunderbird started tanking and wiped all the mails from my mailserver without actually downloading anything.

I could've restored the mails from a backup but instead I figured I'd take my emails offline and use Thunderbird as my primary mail client. I had a backup of my mails from OfflineImap but the problem was that OfflineImap uses the MailDir format and Thunderbird didn't support it.

Luckily Thunderbird did support maildir and I modified an existing MailDir to Mbox converter written in Python to work with Offlineimaps potentially infinitely recursive folder format. Hopefully it helps someone else.

#!/usr/bin/env python
# -*- coding: utf-8 -*-
Shane Dowling, 8 Feb 2013
Frédéric Grosshans, 19 January 2012
Nathan R. Yergler, 6 June 2010

This file does not contain sufficient creative expression to invoke
assertion of copyright. No warranty is expressed or implied; use at
your own risk.


Uses Python's included mailbox library to convert mail archives from
maildir [] to
mbox [] format, icluding subfolder.

See for
full documentation on this library.


To run, save as and run:

$ python [maildir_path] [mbox_filename]

[maildir_path] should be the the path to the actual maildir (containing new,
cur, tmp, and the subfolders, which are hidden directories with names like

[mbox_filename] will be newly created, as well as a [mbox_filename].sbd the

import mailbox
import sys
import email
import os

def maildir2mailbox(maildirname, mboxfilename):
    slightly adapted from,
    Nathan R. Yergler, 6 June 2010
    and Frédéric Grosshans, 19 January 2012

    # open the existing maildir and the target mbox file
    maildir = mailbox.Maildir(maildirname, email.message_from_file)
    mbox = mailbox.mbox(mboxfilename)

    # lock the mbox

    # iterate over messages in the maildir and add to the mbox
    for msg in maildir:

    # close and unlock

#Creates the main mailbox
if not os.path.exists(mboxdirname): os.makedirs(mboxdirname)

# Iterate over all folders
def folder_iterate(dirname, mboxname):
    listofdirs=[dn for dn in os.walk(dirname).next()[1] if dn not in ['new', 'cur', 'tmp']]
    for curfold in listofdirs:
        curpath=os.path.join(*[dn+'.sbd' for dn in curlist if dn])
        if not os.path.exists(curpath): os.makedirs(curpath)
        except OSError:
            print('no maildir folders')
        folder_iterate(os.path.join(dirname,curfold), mboxname)

folder_iterate(dirname, mboxname)

Category: Projects Tagged: mail migration thunderbird python