Letterboxx User Guide

Why Letterboxx Exists

Welcome to your newsletter reading room.

Letterboxx exists because I have been saving, reading, losing, rediscovering, and obsessing over online writing since the late 1990s. RSS feeds, blogs, long-form essays, newsletters, little updates from people doing interesting work: I have always loved that world.

But newsletters landed in the one place that was never built to love them back: the inbox.

An inbox is where chores go. Password resets. Receipts. Dentist reminders. Work threads. Little obligations with sharp elbows. Newsletters are different. They are essays, updates, ideas, deals, dispatches, rituals, and the occasional thing you absolutely meant to read three Tuesdays ago. They deserve a calmer room.

Part of the reason behind Letterboxx goes back to 2002. At the time, I was working in IT, helping manage large Windows deployments with Microsoft SMS and handling antivirus rollouts across the company. Computers were useful, but the work often felt operational: maintenance, patching, cleanup, repeat.

Then I bought a used first-generation iPod on eBay. A few weeks later, I picked up a used G4 iMac.

That was not the most practical family-budget decision. We had a 6-year-old, a 17-month-old, and not a lot of extra money lying around for non-necessities. But my wife has always been amazing about supporting my weird ideas, even when they probably sounded a little ridiculous.

That whole Apple world rewired my brain. The hardware, OS X, the industrial design, the animations, and the feeling that everything had been thoughtfully connected changed what I thought technology could be and what software should be.

For the last 20 years, I have been lucky enough to help build web and mobile software with a lot of talented teams. I love making things with other people. Letterboxx is different because it is the first software product I have released entirely on my own. Nothing but me and my thoughts on what this app should be, what it should look like, and how it should work.

For better or worse, that means every detail was shaped around what I honestly think makes the experience better. Letterboxx can be more personal, more opinionated, more Mac-like, and a little more playful than software usually gets to be.

I built Letterboxx as the newsletter app I wanted: a Mac-first reading library for people who love newsletters but do not want them buried beside urgent mail. Email can keep doing mail. Letterboxx gives newsletters a real home.

So that's it. This is Letterboxx. Newsletters collected instead of scattered. A calm and fully-customizable surface that's thoughtfully built underneath. And a “Mac-assed Mac app” for folks that love to read. I hope you enjoy it.

Chris Anderson, May 2026

How Letterboxx Works

Letterboxx connects to the mail folders you choose and brings newsletter copies into its local library.

Your original messages stay in your connected mail account unless you delete them and then remove them from Letterboxx's Trash. Message read and unread status is a separate account setting, so you can decide whether Letterboxx should keep that status local or share it back to the server.

The names are simple once you see them:

• IMAP account means the mail account Letterboxx connects to.
• IMAP folder means a server mailbox such as INBOX, Newsletters, or Promotions.
• Letterboxx Inbox means the local landing place inside the app.
• Letterboxx means a local folder or category inside the app, not a server folder.

When the distinction matters, this guide says IMAP INBOX for the mail-server folder and Letterboxx Inbox for the local app view.

Read status is configurable per account:

• Local only keeps read and unread changes inside Letterboxx.
• Send to mail server sends local read and unread changes back to the original IMAP folder in the background.
• Sync with mail server also refreshes recent imported newsletters from the server's read status during normal checks.

Letterboxx organization is local. Letterboxxes, favorites, highlights, reminders, Clean View settings, and Auto-Delivery rules are not mail-server folders or rules.

Trash and delete are real cleanup. If a newsletter still has a server reference, trash and empty-trash style actions can affect the original mail account. Make a backup before big cleanup days. Future you deserves the parachute.

Make Letterboxx Yours

Letterboxx should feel like your reading place, not a generic utility window.

Use the defaults and start reading right away. Then, when a little preference appears, follow it. Want a denser list? Do it. Want a warmer reader? Done. Want fewer distractions, different sounds, quieter badges, stronger Clean View, automatic backups, or tidy routing rules? Letterboxx has room for that.

Settings gives you control over:

• Accounts and source folders.
• How often Letterboxx checks for newsletters.
• Dock badge and reminder notification behavior.
• App appearance, sidebar density, reader theme, and Night Vision.
• Newsletter list typography, sender badges, date display, and status icons.
• Sounds for newsletter actions.
• Clean View mode and individual blockers.
• Auto-Delivery rules.
• Backup, restore, and automatic backup.
• Sync status, diagnostics, and maintenance tools.

You do not need to configure all of this on day one. Start with accounts, folders, and reading. Come back to the deeper controls when you know how you want the app to feel.

Choose How Newsletters Arrive

Letterboxx supports Gmail, iCloud, Outlook, DreamHost, and custom IMAP accounts.

For Gmail, use Google sign-in. For other providers, use the IMAP host, port, username, password, and TLS setting your provider gives you. Letterboxx tests the connection before saving, because nobody needs mystery failure as a setup step.

Source folders

Choose only the folders Letterboxx should import from. This is where the calm starts.

When the server returns a folder list, Letterboxx shows a searchable chooser. If a provider cannot return a useful folder list, you can enter folder names manually.

Each selected IMAP folder can route imported newsletters to Letterboxx Inbox or directly into a local Letterboxx. A folder route only decides where imported copies appear inside Letterboxx. It does not move original messages on the server.

Delivery settings

In Settings > General, choose whether Letterboxx delivers automatically on launch and whether it keeps checking while open or waits for manual checks from the newsletter list.

You can also choose what the Dock badge counts: nothing, Inbox only, all newsletters, unread, today, yesterday, this week, last week, or reminders.

Reminder notifications can show subject and sender, subject only, or sender only.

Make The Reader Yours

The reader is where Letterboxx should feel most comfortable. This is the seat by the window.

The reader toolbar keeps the useful things close:

• Highlight navigation and highlight controls.
• Print.
• The Show Clean View button in the reader.
• Message Diagnostics from the diagnostics button.
• Zoom Out, Actual Size, and Zoom In.

Reader themes

Settings > Appearance separates the app shell from the reader, so the library and the reading surface can each have their own mood.

The app appearance can follow the system, force Light or Dark, or use Kitty Cat. Kitty Cat gives the dashboard and sidebar an old-school Aqua-inspired personality, while the selected-message reader stays neutral.

Reader themes are separate:

• Color keeps newsletters close to their normal look.
• Newspaper gives the reader a softer black-and-white treatment.
• E-Ink aims for a warmer, e-paper-like feel.

Night Vision is another layer. It controls how Letterboxx handles newsletter content in darker reading situations. Choose Off, Default, Standard, or Adaptive.

Highlights

Select text in the reader, then highlight it from the toolbar or context menu. Highlights stay with the newsletter so you can return to useful passages later.

Use highlights for the sentences that make you stop for a second: quotes, ideas, recipes, product notes, research fragments, and anything you want to find again.

Make The List Behave

The newsletter list can be quiet, dense, roomy, badge-y, buttoned-up, or somewhere in between.

Settings > Newsletter List lets you adjust:

• List font: San Francisco, SF Rounded, New York, or SF Mono.
• Subject size.
• Row density.
• Sender badge visibility and size.
• Sender name visibility and size.
• Date and time visibility and size.
• Unread, favorite, and reminder status icons.

If you want a dense scanner, turn on details and tighten the layout. If you want the list to feel more like a reading queue, hide some metadata and let the subject breathe.

Settings > Appearance also controls sidebar counts and density, so you can decide whether the sidebar feels like a compact control rail or a softer folder list.

Clean View: Keep The Good Stuff

Clean View is Letterboxx's privacy and clutter-reduction layer.

It filters newsletter HTML before the message reaches the reader. The goal is simple: keep the thing you came to read, and lose as much of the baggage as possible.

Cleaning modes:

• Off applies no content blocking.
• Medium blocks common clutter while keeping most newsletters readable.
• High blocks more, including remote images.
• Custom lets you choose the individual blockers.

Custom controls include page scripts, trackers and ads, autoplay, embeds, and remote images.

Medium is the everyday starting point. High is useful when you want stricter privacy or a newsletter is especially noisy. Off is useful when you want to compare the original.

The Clean View report

When Clean View is set to anything other than Off, Letterboxx cleans newsletters automatically. Use the Show Clean View button in the reader to see what Clean View did for the selected newsletter and adjust Clean View settings from the report.

The report is message-specific. It can show what Letterboxx removed for this newsletter, how the sender and all-time totals compare, and which cleanup categories mattered.

Settings > Clean View carries the broader controls: Cleaning Mode, Content Blocking, Blocking List status, cumulative totals, and Clean View Intelligence details.

The Blocking List can be updated locally from Settings. Letterboxx shows status, last updated time, version, source, verification, and source count when those details are available.

Auto-Delivery: Put Newsletters Where They Belong

Letterboxxes are local folders or categories for your newsletter library. Use them for topics, publications, projects, clients, hobbies, research, shopping, or anything else that makes reading easier.

Auto-Delivery is the satisfying part: new arrivals can sort themselves into the right Letterboxx during import.

Use Auto-Delivery for patterns you trust:

• A publication that always belongs in News.
• Shopping mail that always belongs in Deals.
• Client updates that always belong in one project Letterboxx.
• Hobby newsletters that deserve their own category.

Rules can match all conditions or any condition. Conditions can look at From, To, Cc, any recipient, Subject, Message content, and List-ID. Operators include contains, does not contain, begins with, ends with, and is equal to.

If a selected IMAP folder already routes to a local Letterboxx, that explicit folder route wins for new imports before sender or content Auto-Delivery rules.

Back Up The Good Stuff

Backup & Restore protects your Letterboxx library with encrypted, compressed .lbxxbackup files.

Backups can include newsletters, Letterboxxes, Auto-Delivery rules, highlights, app settings, and saved account passwords when they are available from Keychain for known accounts.

Manual backup is for checkpoints: before a major cleanup, before moving to another Mac, before changing account setup, or whenever the library starts to feel like something you would miss.

Automatic backup can save an encrypted archive when you quit Letterboxx. You choose the folder, how many backup files to keep, and the backup password stored in Keychain.

Restore lets you inspect a backup before applying it. After restore, quit and reopen Letterboxx to finish applying the restored data.

Keep your backup password safe. Letterboxx cannot decrypt an encrypted backup without it.

Message Diagnostics

You do not need diagnostics for everyday reading. They are there for the moments when a newsletter looks strange, a delivery feels off, or you simply want to look at the nerdy details of your newsletter. Message Diagnostics are on the reverse of every newsletter. Tapping its button in the toolbar or using the keyboard shortcut Command-I flips the newsletter around to show you header data, full raw source, the composition of the newsletter showing how much was HTML, CSS, images, and much more.

Message Diagnostics shows the details behind the selected newsletter: sender identity, headers, composition, Clean View changes, raw source context, and unsubscribe information.

Activity Center

Activity Center shows retained app-wide activity, including sync, IMAP, account, backup, trash, and highlight events. The full log can be shown, copied, or cleared.

Tools holds maintenance actions:

• Highlight Logging.
• Repair Highlights.
• Backfill Clean View bytes.
• Backfill raw source for older messages when the server still has it.
• Run a message audit.
• Review, clear, or rebuild the sender-logo cache.
• Show sender-logo candidates in Message Diagnostics.

These tools are there when you need them. Most days, you can happily ignore them and keep reading.

Privacy, Plainly

Letterboxx is local-first, but newsletters come from email, so the app should be plain about what it touches.

At a glance:

• Your newsletter library, folders or categories, highlights, reminders, and Auto-Delivery rules belong to Letterboxx.
• Account passwords and Gmail tokens are stored in Keychain. Some account details may follow you through iCloud when available.
• The newsletter library can use CloudKit-backed storage when available, with a local-only fallback if CloudKit is not available.
• Importing stores local newsletter copies. Your original messages stay in your connected mail account unless you delete them and then remove them from Letterboxx's Trash.
• Message read and unread status sharing is optional per account.

For the formal policy, read the Privacy page.

A Few Friendly Answers

Where does Letterboxx fit with Mail?

Use Mail for personal, work, and conversational email. Use Letterboxx for newsletters you want to read, sort, clean up, highlight, and revisit.

Does Letterboxx move my newsletters out of my mail account?

No. Letterboxx imports local copies from the selected IMAP folders. Folder routes decide where those copies appear in the app.

Does importing mark newsletters read on the server?

No. Importing uses a read-safe fetch. Read/unread exchange only happens if you choose a per-account Read status mode that sends or syncs read status.

Why are old newsletters missing?

Initial import is recent-first. The current first pass is capped to recent messages per selected folder so the app can start quickly. Also confirm the newsletter is in a folder Letterboxx imports from.

Why did Clean View remove something I wanted?

Switch Clean View to Off to compare the original. If you want a middle ground, use Custom and choose the blockers yourself.

Why does unsubscribe open my browser?

Some senders require confirmation on their own unsubscribe page. When one-click unsubscribe is not available, Letterboxx opens the sender's unsubscribe link in your default browser.

Should I back up before removing an account?

Yes. Make a backup before account removal, large cleanup, or restore work. Account and cleanup actions can change what local newsletters remain available.

Learn More

This guide will change as Letterboxx changes. It should always stay plain about what the app reads, what it stores, what it backs up, and which actions can affect mail on the server.

Read the Terms, the Privacy page, or send questions to support@letterboxxsoftware.com.