Split Email Client

tokideveloper · September 28, 2026, 6:54pm

Hello,

Similar to Split GPG, I wonder if it’s possible to split an email client like Thunderbird into to parts: Part A is only available in one qube A, part B only in another qube B.

Part A is only for managing emails (receiving, sending, moving, copying) without parsing their bodies. Part B only shows the email (received or to send) bodies to the user.

Qube A has a firewall allowing only connections to the desired email SMTP/IMAP/POP3/etc. servers. Qube B is a disposable and has no internet connection.

Also, for encrypted emails (OpenPGP, S/MIME), additional qubes might be necessary.

Is it possible to implement this?
Has it already been implemented?
Does it make sense at all?

Best regards,
tokideveloper

ephile · September 28, 2026, 7:15pm

split-protonmail offers something along these lines, splitting send and receive into separate thunderbird appVMs

nexus · September 28, 2026, 9:37pm

Makes a lot of sense. Not sure if anyone has implemented this. Is this a use-case you’re actually interested in? For practical reasons?

qubist · September 29, 2026, 9:24am

I think it makes sense but I am not sure if Thunderbird (or any other client that renders HTML mail) is the best fit. HTML and attachments should be viewed in offline disposables.

parulin · September 29, 2026, 1:21pm

I have not tried it myself but while looking at qusal repo, there was this thing:

github.com/ben-grande/qusal

salt/mail/README.md

main

# mail

Mail operations in Qubes OS.

## Table of Contents

*   [Description](#description)
*   [Security](#security)
*   [Installation](#installation)
*   [Usage](#usage)
    *   [Fetcher](#fetcher)
        *   [fdm Configuration](#fdm-configuration)
        *   [mpop Configuration](#mpop-configuration)
        *   [OfflineIMAP Configuration](#offlineimap-configuration)
        *   [Send Inbox to Reader Qube](#send-inbox-to-reader-qube)
    *   [Reader](#reader)
        *   [Mutt Configuration](#mutt-configuration)
        *   [Send Queue to Sender Qube](#send-queue-to-sender-qube)
    *   [Sender](#sender)
        *   [msmtp Configuration](#msmtp-configuration)

This file has been truncated. show original

Credits to unman:

github.com/unman/notes

SplitMutt.md

master

# Split Mail

I like mutt.
Combined with notmuch, it's one of the best mail readers I know.
Although support for fetching and sending email has been added, at heart mutt is a great MUA.
When I started working with Qubes, one of the first things I did was to see if I could get back to the original use of mutt, and separate out the constituent parts into separate qubes.
Turns out, it's easy.

## Why?
First, it allows us to read and process mail offline in a (relatively) sealed qube.
The attack surface is small.  
Second, it allows us to easily separate fetching and sending mail streams.
We can use different Tor routes, different network interfaces, as we want.  
Third, it's fun, and we can learn a lot about the processes behind messaging, and how to organize things in Qubes.

## What?
Breaking down email processing is simple - first, you fetch mail, then you read or process it, then you send mail.  
So, we use one qube for each task.  
Obviously we want the *mutt* qube to be offline, and we can use disposableVMs as the fetching and sending qubes.
These can be firewalled appropriately to restrict network access to only required servers and ports.

This file has been truncated. show original

tokideveloper · September 29, 2026, 7:49pm

Thank you for all your replies!

@ephile @parulin Thank you for the links! I’ll have a look later on.

@qubist Thunderbird is just an example for an email client. Maybe not ideal.

@nexus I’m interested in what is possible with Qubes OS. And I wonder if “split email client” is a viable concept. I want to tell people about Qubes OS and I want to be prepared for that.

Would it make sense to link to these nice concepts directly from the official Qubes OS documentation? I mean, they are hard to find (okay, I didn’t use search engines …).

parulin · September 30, 2026, 5:31am

I don’t think it would have its place in the official docs. And I don’t know if it is easy to find it through search engines without the perfectly crafted query, so that’s why we have this forum