Back up your IMAP mailboxes with ease!

• General
  • Notable features
  • Currently absent features
• Why a re-implementation
• How to use
  • Note for Windows users
  • Store password in keyring
  • List folders
  • Download
  • Serve - View your backed-up emails
    • Using the mutt command line client
    • Using any email client
    • A note on ports
• Installation
  • Tab completion
• How to contribute
• Licence

General

This is go-imapgrab, a re-implementation of the amazing imapgrab in plain Golang. It is a command line application that can be used to make a local backup of your IMAP mailboxes. See below for how to use.

This software is in a stable state and has been used by the main author to back up quite a few mailboxes already. Development started in early 2022. Contributions are very welcome (see below)! Features will be added on occasion and dependencies will be kept up to date as needed, especially in the case of known vulnerabilities.

Notable features

• download IMAP mailboxes to a local directory following the maildir format
• browse local backups with your favourite email client
• download folders in parallel
• static binary without any additional dependencies
• support for system keyring to store credentials securely
• maildir output fully compatible to the original imapgrab (please open an issue in this repository if you notice incompatibilities)
• tab completion for many shells

Currently absent features

Contributions to these would be welcome. Please reach out before starting to work on any of them.

• output in other formats such as mbox
• password specification via command line argument (use environment variable or keyring for now)
• more than two verbosity levels
• disabling SSL for connections
• change user for download (cf. imapgrab's --localuser flag) to be runnable as root (use sudo instead to change the user for one invocation)
• restoration of a local backup to a server
• local removal of emails that have been removed remotely
• download a single folder with multiple threads

Why a re-implementation

The main author had been using the original imapgrab successfully for quite a while to back up mailboxes. However, the original is implemented in the deprecated Python version 2 and has been abandoned. While there are re-implementations in Python 3, none of them appeared quite complete at the time this project started.

In addition to the above, imapgrab uses the getmail executable to download emails. That executable is also written in Python 2 and lacked a complete re-implementation in Python 3 at the time this project started.

Furthermore, the author had started learning Golang not too long before this project started. Golang is a language that provides static binaries while supporting cross-compilation natively. One advantage of such a setup is that it is very easy to provide executables for systems that would run imapgrab or getmail only with difficulty. Thus, go-imapgrab seemed like a project that is useful while providing opportunities to learn.

Still, this project would not have been possible without the amazing tools imapgrab and getmail, which provided a very solid basis for go-imapgrab. Thank you!

How to use

First, you need to download and install the binary. See installation below for details. Once you have the executable, run go-imapgrab --help to see whether it works. Please open an issue in this repository if you experience problems!

A typical workflow consists of the following four steps:

• store the password for your account in your keyring (optional but recommended)
• list the folders in your mailbox
• download the ones you wish to back up
• view locally stored emails using your favourite email client

Note for Windows users

❗ If you are on Windows, replace any invocation of go-imapgrab by go-imapgrab.exe. This document will omit the .exe extension throughout. ❗

Store password in keyring

You can store your password in your system's keyring to avoid having to define an environment variable every time you invoke go-imapgrab. Note that use of the keyring is mandatory when using the graphical user interface. To store your password in the keyring, simply run the following command:

go-imapgrab login -u "${USERNAME}" -s "${SERVER}" -p "${PORT}"

Then, enter your password at the prompt. Note that the password will not be echoed as you type.

The specification of the port it optional, it defaults to 993. Refer to the documentation of your email provider for the username, server, and port. For Gmail, you can:

• use an application-specific password as password
• provide your email address as ${USERNAME}
• use imap.gmail.com as ${SERVER}
• leave out the port since Gmail uses the default one

The password needs to be specified only once. Every subsequent call to the list, download, or serve commands will use the system's keyring if you do not disable it.

To see the full specification for the login command, run:

go-imapgrab login --help

List folders

Usually, the first step after storing the password in your keyring is to list the folders available in your mailbox. If you did not store the password in your system keyring, you have to assign its value to an environment variable called IGRAB_PASSWORD. On Unix-like systems, the following command is usually sufficient:

export IGRAB_PASSWORD="${PASSWORD}"

To list folders in your mailbox, run:

go-imapgrab list -u "${USERNAME}" -s "${SERVER}" -p "${PORT}"

To disable the keyring, for example if you experience problems or don't have a keyring, add the --no-keyring flag. You will need to provide your password via the environment variable in that case.

Once you see your list of folders, decide which ones you want to download and proceed with the download command (see below).

To see the full specification for the list command, run:

go-imapgrab list --help

Download

The next step is to download the folders you want. For example, to download all folders apart from Gmail-specific ones and the Drafts directory, you can run:

go-imapgrab download -u "${USERNAME}" -s "${SERVER}" -p "${PORT}" \
    -f _ALL_ -f -_Gmail_ -f -Drafts --path "${LOCALPATH}"

For the first run for a mailbox, specify for ${LOCALPATH} a non-existing or empty directory. This is where you will download all folders for this mailbox to. The directory will be created first if it doesn't exist, including all parents.

The above command will result in one directory per folder in ${LOCALPATH} in addition to one meta data file per folder that must not be modified or updates won't work. For every run after the first, specify the very same ${LOCALPATH} if you want to download only missing emails.

As you can see in the above command, you can provide multiple folder specifications via the -f or --folder flag. They are evaluated in order. A folder specification is either

• a literal folder name such as Drafts in the above example
• the literal string _ALL_ to specify all folders
• the literal string _Gmail_ to specify all Gmail-specific folders

A folder specification can optionally start with a minus sign (-), in which case it negates the specification. Thus, -Drafts in the above example deselects that folder, while _ALL_ selects all folders first.

These folder specifications have been taken from imapgrab. In contrast, though, multiple folders are not separated by commas but the --folder flag can be provided several times instead.

By default, all folders will be downloaded in parallel using one thread per folder. The implementation of that feature required one login to the IMAP server for each download thread because of a dependency. Your email provider may disallow multiple logins in quick succession. Thus, you may want to use the --threads flag to limit the number of logins and thus threads downloading in parallel. Parallel downloads are most useful for initial syncs.

To see the full specification for the download command, run:

go-imapgrab download --help

Serve - View your backed-up emails

Using the mutt command line client

There are several options to view your locally backed up emails. If you have access to the mutt email client, in order to view emails for a folder in your mailbox called ${FOLDER}, you can run

mutt -f ${LOCALPATH}/${FOLDER}

Make sure to specify the very same ${LOCALPATH} that you specified when running the download command.

Using any email client

Unfortunately, only very few email clients support viewing locally stored emails. To work around that limitation, go-imapgrab can run as a fully-local read-only IMAP server that any IMAP-compatible email client can connect to. Here, fully local means that only programs on the same machine as the one running go-imapgrab can connect to it.

The following example assumes you are using the Thunderbird email client. The first step is to launch go-imapgrab as a local IMAP server. To do so, run the following command:

go-imapgrab serve -u "${USERNAME}" -s "${SERVER}" -p "${PORT}" \
    --path "${LOCALPATH}"

Make sure to specify the exact same values for ${USERNAME}, ${SERVER}, ${PORT}, and ${LOCALPATH} as you did for the download command for the mailbox you wish to view. By default, the IMAP server will listen for incoming connections on port 30912 on your local machine.

Then, launch your email client and manually configure an email account that:

• uses the IMAP protocol
• does not use encryption
• uses localhost as host/server
• uses the same username and password as the email account you wish to view
• uses the port 30912 (or another one if specified via the optional --server-port flag)

For Thunderbird, that would look like this (note that the first digit of the port number is obscured):

Note that you may have to accept the risk of using an unencrypted connection. As the IMAP server will only accept connections from your local machine, this is acceptable on single-user systems. For Thunderbird, that warning would look like this:

If your email client requires you to specify an outgoing email server, use the same as for incoming email.

To see the full specification for the serve command, run:

go-imapgrab serve --help

A note on ports

Only one service can listen on the same port. Thus, if you wish to view multiple mailboxes at the same time, specify a different port for every invocation of the serve command using the --server-port "${SERVERPORT}" flag.

Installation

Go to the project's release page, select the correct distribution for your system, and download it. Extract the downloaded archive and move the extracted binary to a location that is in your $PATH such as /usr/local/bin. Moving it there will likely require root permissions, e.g. via sudo. From now on, you can simply type go-imapgrab in your terminal to use it!

Tab completion

If you want to set up tab completion for your shell, add the following to your shell's configuration file:

• bash: add to ~/.bashrc:

  [[ -x $(command -v go-imapgrab) ]] && eval "$(go-imapgrab completion bash)"

• zsh: add to ~/.zshrc:

  [[ -x $(command -v go-imapgrab) ]] && eval "$(go-imapgrab completion zsh)"

• fish: add to ~/.config/fish/config.fish:

  if type -q go-imapgrab
    eval (go-imapgrab completion fish)
  end

Using tab completion requires adding go-imapgrab to a directory in your $PATH.

How to contribute

If you have found a bug and want to fix it, please simply go ahead and fork the repository, fix the bug, and open a pull request to this repository! Bug fixes are always welcome.

In all other cases, please open an issue on GitHub first to discuss the contribution. The feature you would like to introduce might already be in development.

Licence

GPLv3

If you want to use this piece of software under a different, more permissive open-source licence, please contact me. I am very open to discussing this point.