A fast, Vim-inspired terminal email client for Maildir folders, written in Rust. Heavily inspired by aerc.

Installation

cargo install --path .

Features

• Threaded email list with tree indentation
• Diff/patch syntax highlighting in email bodies
• Reply, reply-all with quoting, forward, built-in Vim-style compose editor
• Drafts and Trash mailboxes (auto-created if not configured)
• Read/unread tracking, flagging, live search, unread-only filter
• Multiple mailboxes with sidebar, tab-based email viewing
• Move emails or entire threads between mailboxes
• SMTP sending via STARTTLS
• Periodic background sync via a configurable shell command (e.g. mbsync)
• Quick reply templates bound to number keys (1-9, 0)
• GPG decryption and signature verification (PGP/MIME and inline PGP)
• List received attachments and save them to disk
• Send file attachments with filesystem path completion

Configuration

Create ~/.config/kingi/config.toml:

[smtp]
host     = "smtp.gmail.com"
port     = 587
name     = "Name Surname"
username = "you@example.com"
password = "app-password"

[[mailbox]]
label = "INBOX"
path  = "/home/you/Mail/INBOX/"
markers = true  # Enables patch status tracking (merged, reviewed, superseded)

# "Drafts" and "Trash" labels are treated specially.
# If omitted, defaults are created under ~/.config/kingi/.
[[mailbox]]
label = "Drafts"
path  = "/home/you/Mail/Drafts/"

[[mailbox]]
label = "Trash"
path  = "/home/you/Mail/Trash/"

# Optional: run a shell command every N seconds to sync mail.
[sync]
command  = "mbsync -a"
interval = 60

# Optional: Case-insensitive regular expressions that mark a patch as merged.
# If omitted, kingi uses the default lore-cli regexes.
[status]
merged_markers = [
    # Line begins with the action verb, followed by "thanks", a target tree
    # ("to <tree>"), or end-of-statement — e.g. "Applied, thanks",
    # "Merged.", "Pushed to for-next".
    "\\b(applied|merged|pushed)(,?\\s+thanks|\\s+to\\s+\\S+|[.!]|\\s*$)",
    # "thanks, applied" / "thanks merged".
    "\\bthanks,?\\s+(applied|merged|pushed)\\b",
    # "patchset applied", "series merged" as a line-leading statement.
    "\\b(patch(set|es)?|series)\\s+(applied|merged)(,?\\s+thanks|\\s+to\\s+\\S+|[.!]?\\s*$)",
    # "Thanks ... merged" / "Thanks ... pushed"
    "\\b(T|t)hanks.*(merged|applied|pushed)",
]

A plain-text ~/.config/kingi/signature file, if present, is appended to every draft.

Quick replies

Place template files named reply-1 through reply-9 and reply-0 in the config directory (~/.config/kingi/). Pressing the corresponding number key on an email opens a reply pre-filled with that template's content.

For example, create ~/.config/kingi/reply-1:

Thanks for the patch, applied!

Then press 1 on any email to reply with that text.

GPG

Kingi automatically detects and decrypts PGP-encrypted emails and verifies PGP-signed emails when opened. Both PGP/MIME (RFC 3156) and inline PGP formats are supported. Encrypted emails are marked with a ⚷ icon in the thread list.

A working gpg-agent is required for passphrase handling. To override the GPG binary path:

[gpg]
binary = "gpg2"

Attachments

Kingi supports sending and receiving file attachments. Attachment lists show filenames and sizes. Received files can be saved to disk without overwriting existing files, including attachments in PGP/MIME emails after decryption.

The compose editor supports adding and removing files, with filesystem path completion for relative, absolute, and home-directory paths. Attached files retain their contents even if the original files change. Saved drafts preserve attachments, and send or save errors keep the message available for retry.

Key bindings

Thread list

Key	Action
r / R	Reply-all / reply-all quoted
1-9, 0	Quick reply with template
f	Forward
C	Compose new email
/ / Esc	Search by subject / clear
\ / Esc	Search by sender / clear
m / M	Move email / move entire thread
D	Delete email
Enter	Open email (in Drafts: reopen in editor)
v	Toggle read / unread
Ctrl+f	Toggle flagged
Ctrl+x	Toggle merged
Ctrl+A	Mark all emails as read
j/k/↑/↓	Move selection
Ctrl+D/Ctrl+U	Page down / up
g / G	First / last email
J / K	Next / previous mailbox
s	Toggle sort order
V	Toggle unread-only filter
F	Toggle flagged-only filter
Ctrl+S	Force sync
?	Help
Q	Quit

Email tab

Key	Action
r / R	Reply / reply quoted
1-9, 0	Quick reply with template
f	Forward
Y	Copy body to clipboard
a	List / save attachments
m / M	Move email / move thread
Ctrl+f	Toggle flagged
Ctrl+x	Toggle merged
D	Delete and close tab
j/k/↑/↓	Scroll line
Ctrl+D/Ctrl+U	Page down / up
g / G	Top / bottom
J / K	Next / previous email
?	Help
q	Close tab

Compose

Key	Action
Ctrl+Q	Send dialog
Ctrl+A	Manage attachments
j/k	Navigate dialog options
Enter	Confirm (Send / Save draft / Discard)
Esc	Back to editor

Global

Key	Action
Ctrl+N / Ctrl+P	Next / previous tab

History

This project started with the aim of learning more about the Rust programming language. Over the 2025 Christmas holidays, I set myself a challenge: design an algorithm to load n emails from a Maildir and reconstruct their threads in O(n) time. Each thread forms a tree, with emails as nodes and replies linked to their parent messages.

That challenge led to learning Rust's shared memory management, fighting with the borrow checker, and achieving C-like performance. It was a lot of fun, even if the borrow-checker struggle is very real.

Around March–April 2026, the emergence of more capable LLMs, such as Opus 4.6, made it possible to speed up development and tackle a task I hadn't been able to finish due to work and personal commitments: writing a proper UI around that algorithm.

It worked, but with a caveat: LLMs produced tons of bad code. I had to work through that, learning how to use these new tools effectively while adding all the features I had always wanted in a terminal email client: keybindings similar to aerc, fast loading speeds, and a workflow tailored for mailing-list patch reviews (LTP and the Linux kernel in particular).

In the end, it worked out. kingi became my primary terminal email client: fast, easy to use, shaped around my workflow, and with unique features no other client offered. This is the best email client I have ever used, and I want to share it with everyone who is willing to try it out.