qtmaildir

A Qt6 desktop mail client for reading and organizing a local, notmuch-indexed Maildir. A GUI counterpart to neomutt for the parts of mail handling that are easier with a mouse and a real HTML renderer.

What it does not do

This is the important half of the description.

qtmaildir does no network protocol work at all. There is no POP, no IMAP, no SMTP, and no sync implementation. Mail arrives in your Maildir by whatever you already use (mbsync, offlineimap, fetchmail) and is indexed by notmuch new. qtmaildir reads the result.

Fetching is delegated to a command you configure. Running your existing script means joining the flock that already serializes it against cron; a built-in implementation would sit outside that lock and could run two mbsync processes over one Maildir, which corrupts UID state.

Sending is not implemented. Compose, reply, forward and send are planned for v2 and need a companion send script that does not exist yet.

There is also no dry-run and no "are you sure?" on destructive actions. The answer for a human at a GUI is undo, which is implemented, and which is strictly better than a dialog that gets dismissed reflexively.

Requirements

Verified against these versions on Slackware -current:

Component	Version	Notes
Qt6	6.11.1	Widgets and WebEngine. On Slackware both ship in the monolithic `qt6` package; there is no separate `qt6-webengine`.
libnotmuch	0.39 (libnotmuch 5.6)	Installs no `notmuch.pc`, so CMake locates it with `find_path`/`find_library` rather than pkg-config.
GMime	3.2.15	Does ship `gmime-3.0.pc`.
CMake	4.3.4	3.21 or newer.
GCC	15.3.0	C++17.

You also need a notmuch database that is already set up and working from the command line. qtmaildir does not create or configure one.

Building

cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build
./build/src/qtmaildir

Running the tests:

ctest --test-dir build --output-on-failure

A single test binary, for a tighter loop:

./build/tests/test_keymap

Packaging builds do not need the tests, and building them pulls in Qt6::Test to produce nothing that ships:

cmake -S . -B build -DQTMAILDIR_BUILD_TESTS=OFF

Slackware package

assets/slackbuild/ holds a SlackBuild. It follows SBo conventions, with two deliberate departures: the tag is _danix rather than _SBo, and the package type is txz rather than tgz, since this is not an SBo submission. sbolint reports exactly those two as errors and nothing else.

cd assets/slackbuild
# fetch the source tarball named in qtmaildir.info next to the script
sudo ./qtmaildir.SlackBuild

notmuch is the only dependency outside Slackware itself; Qt6 (WebEngine included), gmime and cmake are all stock.

Configuration

~/.config/qtmaildir/qtmaildir.conf, INI format.

The Maildir path is deliberately not configurable. notmuch already stores it as database.path and libnotmuch reads it; duplicating it here would create two sources of truth and let the GUI index a different tree than the CLI. The only escape hatch is pointing at an alternate notmuch config, so notmuch remains the authority either way.

Per-account subdirectories are configured, because notmuch does not model accounts at all: it sees one flat tree. An account is a path prefix plus an identity.

[general]
; Optional. Omit to let notmuch resolve its own config, which is what keeps
; the GUI and the CLI pointed at one database.
; notmuch_config = /home/you/.notmuch-config
; Optional. Starting zoom of the message pane, 0.5 to 3.0. Only the starting
; point: once you zoom with Ctrl+wheel or Ctrl+/Ctrl-, that is remembered
; separately and this value no longer applies.
; message_zoom = 1.0
; Optional. Which [queries] entry to open at startup, by name. Defaults to
; Unread. Falls back to the first saved query if no query by this name
; exists, and warns if you named one explicitly.
; startup_query = Unread
; Optional. Open the completion popup as soon as an empty query bar takes
; focus, without pressing the shortcut. Defaults to false.
; completion_on_focus = false
; Optional. How long an opened thread stays unread before it is marked read,
; in milliseconds. Defaults to 2000. Zero marks it read at once; any negative
; value turns the behaviour off, leaving threads unread until you toggle them
; with Ctrl+U. Arrowing quickly through a list marks only the thread you stop
; on, never the ones you pass through.
; mark_read_delay_ms = 2000
; Optional. What to do about unsynced tag changes when you quit. "ask" (the
; default) offers to sync, quit anyway, or stay; "always" syncs without asking
; and quits when it finishes; "never" quits silently. A sync that fails never
; closes the window, so a failure cannot discard the changes quietly.
; sync_on_exit = ask

[completion]
; Optional. Extra content types offered after mimetype:, APPENDED to the
; built-in list rather than replacing it, so a typo here cannot leave you
; with fewer completions than the defaults.
; Entries are separated by ',', and within an entry '|' separates the value
; from its optional description. The two characters differ because QSettings
; splits comma lists itself, so a description containing a comma would
; otherwise be read as two entries. Neither character is legal in a mimetype.
; extra_mimetypes = application/vnd.oasis.opendocument.text|ODT document, message/rfc822|forwarded mail, text/calendar

[sync]
; Optional. Omit and the Sync button disables itself with a tooltip.
; assets/mailsync.sh is the reference implementation; see "The sync command".
; command = /home/you/bin/mailsync.sh

; Section names use a dot, not a slash: QSettings treats "/" as its own
; group separator, so [account/work] would be parsed as a nested group.
[account.work]
name = Your Name
address = you@example.org
maildir = work-mail        ; relative to notmuch's database.path
drafts = Drafts            ; recorded for v2; unused today
label = W                  ; optional chip text; defaults to the key
color = #2f6fa8            ; optional chip colour; generated when unset
channel = work             ; optional mbsync channel; defaults to the key

[account.personal]
name = Your Name
address = you@example.net
maildir = personal
drafts = Drafts

[tagcolors]
; Optional. Colours resolve by exact tag first, then by top-level prefix, so
; one entry covers a whole hierarchy.
shopping = #3366cc         ; also colours shopping/amazon, shopping/nike, ...
shopping/amazon = #ff9900  ; ... unless the exact tag overrides it
work = #cc4444

[queries]
Inbox = tag:inbox
Unread = tag:unread
Flagged = tag:flagged

[keys]
Ctrl+E = archive
Ctrl+D = delete
j = next_thread
k = prev_thread

Saved-query buttons appear in alphabetical order rather than file order: QSettings returns keys sorted, and preserving file order would mean hand-rolling an INI parser. Which query opens at startup is therefore a separate setting, [general] startup_query, rather than "the first one".

The query bar

The bar at the top takes a notmuch query and shows the matching threads. Saved queries from [queries] sit beside it as buttons.

Completion helps with the syntax rather than replacing it. Ctrl+Space opens the popup, and ordinary typing keeps it up to date. Candidates carry a short description on the right, and matching is on substrings, so typing amazon still finds shopping/amazon.

What completes:

Prefixes. tag:, from:, date:, mimetype: and the rest, each with a one-line description of what it matches, plus the and, or and not operators.
Tag names, after tag: and after is:, which notmuch treats as the same thing. The list is the real set of tags in your database, refreshed at startup, after a sync, and whenever tagging introduces a new one.
Dates, after date:. today, last_week and similar, on either side of a .. range independently, so date:last_month..today can be completed a bound at a time. Entries that are ranges in themselves, like 1week.., are withheld once a range is already being written.
Content types, after mimetype:, from a short built-in list you can extend through [completion] extra_mimetypes.
Account directories, after path:, in both the plain and the recursive <maildir>/** form.

from:, to:, subject:, folder:, attachment:, thread: and id: offer no values. Addresses and folder names would need an enumerator libnotmuch does not expose, and the rest are free text.

notmuch's date parser also accepts free-form dates such as 2026-01-15 or 15/01/2026..today. Those cannot be offered as candidates, since there is no finite list of them, so the date popup carries a footer line saying so. Type them and they work; the popup simply has nothing to suggest.

Attachments

A paperclip in the leftmost column of the thread list marks threads that carry an attachment, so it is visible without opening the thread. It comes from the attachment tag notmuch applies while indexing, not from parsing the message, and costs no extra query.

Tagging

Archive, delete, spam, flag and toggle-unread write fixed tags. For anything else, Ctrl+T opens a dialog over the selected threads: type tags to add or remove, separated by commas, or clear a checkbox to drop a tag already present.

Both fields complete against every tag in your database, which is a guard against typing shoppping beside shopping, not a restriction: a tag that does not exist yet is exactly what the dialog is for, so any valid name is accepted.

With several threads selected, a tag on only some of them shows a partially checked box saying how many. Leaving it alone changes nothing. Check it to apply it to all, clear it to remove it from all.

Tag names are rejected if empty, if they start with - (notmuch reads that as "remove this tag"), or if they contain spaces or unprintable characters. The dialog says which name was refused and why, and applies nothing until the whole set is valid.

Every change goes on the undo stack, so Ctrl+Z reverses a mistyped tag.

The sync command

qtmaildir does not fetch mail. [sync] command names a script it runs as a subprocess, and assets/mailsync.sh is the reference implementation: mbsync -a followed by notmuch new, under a flock so a cron timer and a click here cannot run two mbsync processes over one Maildir.

ln -s "$PWD/assets/mailsync.sh" ~/bin/mailsync.sh

A symlink rather than a copy, so the same script serves cron and the running application and there is only one of it to edit.

It writes to ~/.local/state/mailsync.log itself, so a caller must not redirect into that file as well. The obvious crontab line is the wrong one:

*/10 * * * * ~/bin/mailsync.sh                       # right
*/10 * * * * ~/bin/mailsync.sh >> mailsync.log 2>&1  # every line twice

Rotation is left to logrotate, which does it better than a shell script can. An earlier version rotated by size on its own and fought /etc/logrotate.d/ over the same file, overwriting a compressed generation with an uncompressed one.

Two things any replacement has to get right, both learned the hard way:

Print to stdout as well as any log file. qtmaildir shows what the command prints. A script that redirects its own output to a log leaves the sync pane empty, which is what the previous version of this one did.
Exit non-zero when the sync failed. qtmaildir believes the exit status: it reports success, clears the unsynced-changes count, and will quit on it during a sync-on-exit. The previous version ended in an unconditional exit 0, so a failed mbsync was indistinguishable from a clean run.
Exit 75 when another run holds the lock, rather than 1. A skip is not a failure: the other run is doing the work, and with a timer every ten minutes a click landing inside one is routine. qtmaildir reports 75 as "a sync is already running" and leaves the log pane alone, where any other non-zero code raises an error.
Accept channel names as arguments, and sync everything when given none. qtmaildir passes the mbsync channels of the accounts it has edited, so a sync after tagging one account's mail does not fetch all of them. A script that ignores its arguments still works, it just always syncs everything.

Per-account sync

When tag changes are outstanding, a sync passes only the affected accounts' channel names to the command. When nothing is outstanding the run is a plain fetch and no names are passed, so every account is synced: narrowing a fetch to wherever the last edit happened to be would quietly stop collecting mail everywhere else.

The name passed is the mbsync channel, which is not always the account's section key. [account.mail-first.last] may well be the channel mail-firstlast, since a section key can carry dots that the channel does not. Set channel in the account section wherever the two differ:

[account.mail-first.last]
maildir = mail-first.last
channel = mail-firstlast

Getting this wrong is not silent: mbsync fails on a channel it does not know, and qtmaildir reports the sync as failed rather than clearing the count. An account tag with no matching section falls back to syncing everything, since skipping it would strand its edits with nothing to say so.

While a sync this window started is running, the status bar shows an indeterminate progress bar. It is deliberately not a percentage: mbsync reports no progress, so a bar filling left to right would be inventing one. A sync started outside the application, by your cron timer, is not currently visible here at all.

Unsynced changes

Tagging changes the notmuch index at once, but the mail store only learns about it on the next sync. The status bar therefore counts the tag changes made here that a sync has not yet carried over, and clears the count when one succeeds. A failed sync leaves the count standing, since the changes really are still unsynced.

The count is a lower bound rather than a guarantee: an external notmuch new from your own cron can carry changes over without this application noticing.

Quitting with changes outstanding asks what to do, controlled by [general] sync_on_exit. See the configuration block above for the three values. When a sync started at exit fails, the window stays open and says so rather than quitting as though it had worked.

Message details

The strip above the message pane says what it can say without guessing. A thread holding one message shows its From, To and Cc under the subject. A thread holding several shows the subject and the message count only: From, To and Cc differ from message to message, and once you have replied there is no single recipient the thread is addressed to, so naming one would be a guess dressed as a fact.

The Details... button beside the subject, or Ctrl+Shift+D, opens the full headers of every message in the thread, numbered, as read-only plain text.

Under the message pane, one Attachments (N) button opens a list of the thread's attachments: which message each came from, its filename and its size, with a Save for each. With more than one, Save all writes them into a new subfolder named <date> <subject> inside a folder you choose. The subfolder is named in the picker before you commit to a location, and an existing folder of that name is never merged into.

Filenames in a message are untrusted, so what is displayed and written is always a sanitised basename: an attachment named ../../etc/passwd is written inside the folder you chose and nowhere else. Where several messages in a thread attach the same filename, later ones get a numeric suffix rather than overwriting the earlier file.

Opening an attachment in its default application is deliberately not offered. Handing a file from a stranger to xdg-open is a different security decision from writing it where you asked, and is not one this program makes for you.

Keybindings

Defaults, all rebindable through [keys]:

Key	Action	Does
`Ctrl+J`	`next_thread`	Select the next thread
`Ctrl+K`	`prev_thread`	Select the previous thread
`Return`	`open_thread`	Focus the thread list
`Ctrl+E`	`archive`	Remove `inbox` from every selected thread
`Ctrl+D`	`delete`	Add `deleted`
`Ctrl+Shift+S`	`spam`	Add `spam`, remove `inbox`
`Ctrl+U`	`toggle_unread`	Toggle `unread`
`Ctrl+Shift+U`	`mark_all_read`	Remove `unread` from every thread in the view
`Ctrl+I`	`flag`	Add `flagged`
`Ctrl+L`	`focus_query`	Focus and select the query bar
`Ctrl+Space`	`complete_query`	Focus the query bar and offer completions
`Ctrl+H`	`toggle_html`	Switch the thread between HTML and plain text
`Ctrl+M`	`load_remote`	Load remote images for the current thread
`Ctrl+T`	`edit_tags`	Add or remove any tag on the selected threads
`Ctrl+Shift+D`	`message_details`	Show the full headers of every message in the thread
`Ctrl+Z`	`undo`	Undo the last tag change
`Ctrl+G`	`sync`	Run the configured sync command
`Ctrl+Q`	`quit`	Quit

Every action now carries a default binding, and every one appears in a menu. Help > Keyboard shortcuts lists the current bindings, generated from the actions themselves, so it shows your overrides rather than these defaults.

An unknown action name in [keys] produces a warning at startup rather than binding silently, so a typo is visible.

Upgrading from 0.1.0

0.1.0 used single letters (j, k, a, d, N, F, h, u, G, /). Those still work if you keep them in [keys], and single letters remain safe to bind: Qt suppresses a plain-letter shortcut while the query bar has focus, so typing a query is unaffected.

Three of the old defaults never actually fired. Typing a capital sends Shift+the key, but N, F and G were stored as the unshifted key, a combination no keystroke produces, so toggle_unread, flag and sync were dead. A bare capital in [keys] is now read as Shift+that letter, which is what you press, so those bindings work whether you keep the old names or move to the new defaults. Note this makes y and Y two different keys.

Tag actions apply to every selected thread, not only the focused one.

Security posture of the message view

A mail client rendering HTML is a browser engine pointed at input from strangers, and it is treated that way.

A dedicated off-the-record QWebEngineProfile: no cookies, no cache, nothing persisted.
JavaScript disabled. LocalContentCanAccessRemoteUrls and LocalContentCanAccessFileUrls both false. Plugins and fullscreen off.
A request interceptor that blocks everything by default. Remote images, stylesheets and fonts are stopped before a connection opens, which defeats tracking pixels and read receipts.
When something was blocked the header shows "Remote content blocked" with a Load remote content button. The grant applies to that one render and is never remembered. Switching threads discards both the grant and anything already fetched under it.
Link clicks are intercepted and handed to the system browser, so a message can never replace the pane with a page of its own choosing.
A whole thread renders as one document rather than one web view per message, which would spawn a Chromium render process per message. Sharing one document means cid: references could collide between messages, so every reference is namespaced per message; two newsletters using cid:logo@example.org resolve to their own images.
Attachment filenames are treated as untrusted input. A name from a MIME header is reduced to its basename and the result is resolved against the chosen directory; anything escaping that directory is refused.

Documentation

CHANGELOG.md - what changed in each release.
docs/RELEASING.md - versioning policy and the release steps.
docs/manual-verification.md - results of the manual checklist run against a real mailbox, including the defects it caught.

License

GPL-2.0-only. See LICENSE for the full text.

Bundled fonts

Two fonts are bundled under assets/fonts/, both licensed SIL Open Font License 1.1, which is compatible with the GPL and permits redistribution. Each ships with its own licence text beside it.

Font	Used for	Licence
Oxanium ExtraBold	the `qtMailDir` wordmark	`assets/fonts/OFL-Oxanium.txt`
IBM Plex Sans Regular	the placeholder pane's text	`assets/fonts/OFL-IBMPlexSans.txt`

Both are subsets, not the complete fonts, because they are embedded into a rendered document as data URIs and the whole family would be far larger than the page using it. Oxanium is instanced to weight 800 and cut to the nine characters of the wordmark, 43K down to 1.2K. IBM Plex Sans is cut to Latin-1 plus common punctuation rather than to the exact strings in use, 525K down to 13K: it carries interface text that will change, and a subset matching only today's wording would break the moment a string is edited.

To regenerate either after changing what is drawn:

fonttools varLib.instancer Oxanium[wght].ttf wght=800 -o Oxanium-800.ttf
pyftsubset Oxanium-800.ttf --text="qtMailDir" --flavor=woff2 \
    --layout-features='' --desubroutinize \
    --output-file=assets/fonts/Oxanium-ExtraBold-subset.woff2

Development Approach

This project is developed using AI-assisted tools. Code is generated with the help of AI based on human-provided specifications, design decisions, and iterative feedback.

All contributions are reviewed, tested, and curated by the maintainer before being included in the codebase. AI is used as a productivity and exploration tool, while human oversight remains central to all decisions.

The goal is to combine the flexibility of AI-assisted development with standard open-source practices such as transparency, review, and accountability.