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Mailfile: Encrypted File Storage in IMAP
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python-mailfile: Encrypted IMAP File Storage

This library implements a simple "filesystem" inside an IMAP folder. The filesystem can be symmetrically encrypted (using the cryptography library's AES-128 Fernet construct), it supports concurrent readers/writers and file versioning.

Due to the fact that file data must live entirely in RAM and be transmitted in its entirety over the network after every change, Mailfile is not well suited for very large files. Please also be considerate towards the IMAP server admin!

The motivation for this tool is that an IMAP account is the most commonly available form of standards compliant "cloud storage" available to the general public. This makes an IMAP account a compelling location for app backups or basic synchronization, and Mailfile's sister project, Mailpile, needs exactly such features...

Other storage solutions that present the same API as Python's imaplib should work as well. Included is one such solution, backends.FilesystemIMAP, which reads/writes from files on disk using a variant of the Maildir format.

See the doc-strings for Mailfile.synchronize for a description of the protocol itself and Mailfile.encode_object to read about the message format in IMAP.


You will need:

  • Python 2.7
  • cryptography

If you want to mount your Mailfile using FUSE, you also need:

  • fusepy

Shell examples

These all do roughly what you would expect:

python -m mailfile help

python -m mailfile login

python -m mailfile put /project/

python -m mailfile ls /

python -m mailfile mount /path/to/mountpoint

python -m mailfile logout

Code example

from imaplib import IMAP4
from mailfile import Mailfile

mailfile = Mailfile(IMAP4('', 143), 'MAILFILE_DATA')

# This is the key used to encrypt/decrypt our data

# Do whatever IMAP authentication dance you need, see imaplib.

with mailfile:
    with'/magic/path/name.txt', 'w') as fd:
        fd.write('hello world')

    # Trying to read the file here would fail, unless we sync state:

with'/magic/path/name.txt', 'r') as fd:


  • Python 3
  • Add an info command to the CLI, to get your encryption key etc.
  • Should we hard-code in a max file size and error out?
  • Recovery: synchronize mode that ignores snapshots
  • Does append mode work or make sense?
  • Data injection attack: prefer mode that requires encryption?
  • More testing: does it work with the popular IMAP servers?
  • Implement CLI put --recursive command
  • File locking would be nice

Copyright, license, credits

This code is: (C) Copyright 2019, Bjarni R. Einarsson

Mailfile is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Mailfile is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with mailfile. If not, see

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