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Lightweight, asynchronous IMAP serving in Python.

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Lightweight, asynchronous IMAP serving in Python.

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This project attempts to simplify the complexity of the IMAP protocol into a set of clean Python APIs that can be implemented by pluggable backends. Everything runs runs in an asyncio event loop.

There are two backend plugins included in the package, dict and maildir.

API Documentation

Table of Contents

Install and Usage

$ pip install pymap
$ pymap --help
$ pymap dict --help
$ pymap maildir --help

dict Plugin

The dict plugin uses in-memory dictionary objects to store mail and metadata. While the server is running, all concurrent and future connections will see the same data, including added and removed messages, but no changes will persist if the server is restarted.

You can try out the dict plugin with demo data:

$ pymap --insecure-login --debug dict --demo-data

In another terminal, connect to port 1143 and run some commands:

. login demouser demopass
. OK Authentication successful.
. select INBOX
* OK [PERMANENTFLAGS (\Answered \Deleted \Draft \Flagged \Seen)] Flags permitted.
* FLAGS (\Answered \Deleted \Draft \Flagged \Recent \Seen)
* OK [UIDNEXT 105] Predicted next UID.
* OK [UIDVALIDITY 4097774359] UIDs valid.
* OK [UNSEEN 4] First unseen message.
. OK [READ-WRITE] Selected mailbox.
. logout
* BYE Logging out.
. OK Logout successful.

Here are some other commands to try:

. uid fetch 1:* all
. list "" ""
. create "A New Folder"
. store * +FLAGS (\Deleted)
. expunge

maildir Plugin

The maildir plugin uses on-disk storage for mail and metadata. For mail data, it uses the eponymous Maildir format. However, since Maildir alone is not enough for modern IMAP usage, it is extended with additional data as described in Dovecot's MailboxFormat/Maildir, with the intention of being fully compatible.

For login, the plugin uses a simple formatted text file, e.g.:


The colon-delimited fields are the user ID, the mailbox path, and the password. The mailbox path may be empty, relative, or absolute. An empty mailbox path will use the user ID as a relative path.

Try out the maildir plugin:

$ pymap --insecure-login --debug maildir /path/to/users.txt

Once started, check out the dict plugin example above to connect and see it in action. The biggest difference is, when stop and restart the pymap server, your mail messages remain intact.

Supported Extensions

In addition to RFC 3501, pymap supports a number of IMAP extensions to give clients easier and more powerful use.

RFC 2177

Adds the IDLE capability and command, which lets clients wait (without issuing commands) and receive mailbox updates as they happen without polling.

RFC 3502

Adds the MULTIAPPEND capability, allowing multiple messages to be atomically appended to a mailbox with a single APPEND command.

RFC 3516

Adds the BINARY extension, providing better support for the encoding and transfer of binary data.

RFC 4315

Adds the UIDPLUS capability, which adds the UID EXPUNGE command and defines the APPENDUID and COPYUID giving clients more insight into the messages added to a mailbox.

RFC 4466

No additional functionality by itself, but allows pymap to be extended easily and more robustly handle bad client implementations.

RFC 7889 (partial)

Adds the APPENDLIMIT= capability, declaring the maximum message size a server will accept from an APPEND command. Mailbox-specific limitations defined by the RFC are not supported.

Development and Testing

You will need to do some additional setup to develop and test plugins. First off, I suggest activating a virtualenv. Then, install the test requirements and a local link to the pymap package:

$ pip install -r test/requirements.txt
$ pip install -e .

Run the tests with py.test:

$ py.test

If you intend to create a pull request, you should make sure the full suite of tests run by CI/CD is passing:

$ py.test --mypy --flake8 --cov=pymap

A py.test run executes both unit and integration tests. The integration tests use mocked sockets to simulate the sending and receiving of commands and responses, and are kept in the test/server/ subdirectory.

Type Hinting

This project makes heavy use of Python's type hinting system, with the intention of a clean run of mypy:

mypy pymap

No code contribution will be accepted unless it makes every effort to use type hinting to the extent possible and common in the rest of the codebase. There is no need to attempt --strict mode.

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