RustBox/docs/FEATURES.md

RustBox features

RustBox is a self-hosted webmail for any standards-compliant IMAP/SMTP server. It ships as one Rust executable with the whole interface built in. The interface is available in English and Polish.

Contents

• Mail
• Composing
• Search, labels and contacts
• Filters (Sieve)
• Calendar
• Notifications and realtime
• Appearance
• Mobile
• Security and privacy
• Administration and deployment
• Known limitations

Mail

• Three-pane layout (folders, message list, reader) with resizable panes. The preview can sit on the right or at the bottom, or be turned off.
• Folder tree with subfolders shown under their parent and collapsible branches. You can create, rename, delete and subscribe to folders, mark all as read and empty a folder.
• Special folders (Sent, Drafts, Trash, Junk, Archive) are configured per account. They follow renames, and administrators can set server-wide defaults.
• Accurate total and unread counters, kept in sync with the mail server. Changes appear immediately and are reconciled in the background.
• Threaded or flat reading, previous/next navigation, and automatic opening of the next message after a move or delete.
• Bulk actions on many messages at once, including the whole search result: read/unread, flag, archive, move, copy, label, spam and delete.
• Drag and drop a message onto a folder to move it. Moves and deletes can be undone.
• Snooze: hide a message until a chosen time, then see all snoozed messages in one list.
• Pagination (up to 300 per page), progressive loading or loading the whole folder. Sort by date, sender, subject or size, and optionally keep flagged messages on top per folder.
• A compact single-line row layout when the message list is wide.
• Safe HTML preview in an isolated frame. Remote images are blocked until you allow them, or loaded only for contacts or trusted senders.
• Attachment preview for images, PDF, text, HTML and video. You can download one attachment or all of them as a ZIP.
• Raw headers, message source, .eml download and .eml import into any folder.
• One-click unsubscribe from mailing lists when the sender supports it.
• A short context menu with submenus (forward, labels, snooze, filters, sender, more), designed to always fit the window.
• Mailbox quota with warnings at 80% and 95%.
• Several accounts signed in at the same time in one browser, with quick switching.

Composing

• HTML, plain-text and Markdown editors. The HTML toolbar covers fonts, sizes, colours, lists, quotes, alignment, links, undo and redo.
• Inline images: paste or drag and drop them, then resize, align and crop in place.
• Attachments by drag and drop, with upload progress and a reminder when the text mentions an attachment that isn't there.
• Drafts are saved automatically and can be recovered. Drafts from the Drafts folder, including ones written in other mail clients, open directly for editing.
• Undo Send: a short window to cancel a message after pressing Send.
• Multiple identities, each with Reply-To, automatic Bcc, organisation and text/HTML signatures. Replies pick the matching identity automatically.
• Priority, read-receipt requests and recipient autocomplete from contacts.
• Forward as attachment.
• OpenPGP: key management, signing and encryption (PGP/MIME and inline), decryption and verification, and key discovery.

Search, labels and contacts

• Full-text search with operators (from:, to:, subject:, folder:, has:attachment, is:unread, is:flagged, dates). Matching terms are highlighted, searches can be saved and there is an advanced search dialog.
• Coloured labels with bulk assignment. They can optionally be kept in sync with IMAP keywords, so they are visible in other clients.
• Contacts with photos, several e-mail addresses, phone numbers and postal addresses, plus groups, duplicate detection and merging.
• vCard import and export, including importing a vCard straight from a message.

Filters (Sieve)

RustBox manages server-side filters over ManageSieve, the standard used by Dovecot Pigeonhole and others.

• Visual rule editor: conditions on sender, domain, recipients (To/Cc, To only, Cc only), subject, mailing list, any header, message size, attachments and priority. Conditions can be joined with AND/OR and negated, and a rule can have exceptions ("except if…").
• Actions: move, copy, move to Trash, add a label, mark as read, flag, redirect (optionally keeping a copy) and discard. A rule can run several actions and stop processing further rules.
• Templates for common rules: messages from a sender to a folder, subject words, flagging mail from a VIP, newsletters, mail sent to an alias, large attachments, forwarding a copy.
• Apply now: a rule normally affects only new mail. "Check matches" shows how many messages already in a folder match it, and "Apply now" runs its actions on them. Each rule in the list also has its own "Apply now".
• Always move messages from this sender… straight from the message context menu, and quick filters created from a message's sender, domain or subject.
• Offers to create a target folder that does not exist yet.
• Every rule is summarised in plain language ("When … Then …") and shown with a live preview of the generated script.
• Out-of-office replies with optional start and end dates, plus a raw script editor with server-side validation, backup and restore.

Calendar

• Month, week, day and agenda views.
• Events with all-day mode, location, attendees, status, colour and a meeting link.
• Two reminders per event (for example 15 minutes and one day before), with default reminders for new events. Reminders for all-day events fire at the start of the working day.
• ICS import and export, including importing an invitation attachment.
• Optional CalDAV/CardDAV server ([dav]): the same calendar and contacts sync with phones, Thunderbird, DAVx⁵, Apple Calendar/Contacts or an ActiveSync gateway such as ActivePush. See CALDAV_CARDDAV.md.

Notifications and realtime

• New mail shows up immediately thanks to IMAP IDLE and a live connection to the browser.
• Desktop notifications with an optional sound, a choice of folders to watch and Do Not Disturb hours.
• The unread count appears in the browser tab and, where supported, on the app icon.

Appearance

• Light, dark, system or time-of-day theme.
• 43 interface styles:
  • RustBox and classic styles;
  • Roundcube Classic, Larry and Elastic;
  • styles inspired by popular mail clients and apps;
  • editor themes such as Nord, Dracula, Catppuccin, Solarized, Gruvbox and Tokyo Night;
  • atmospheric styles;
  • retro styles: Windows XP, Mac OS X Aqua, iOS 6, Windows 7, Frutiger Aero and BeOS.
• Style depth:
  • colours only;
  • standard, which adds the style's layout;
  • immersive, which also adds the style's shapes, typography, app bar and backdrop.
• An optional Style gradients switch.
• A predefined style's layout and typography can be adjusted while it keeps its look. Changing a colour creates a custom copy.
• The RustBox custom style is fully adjustable: colours, fonts, sizes, density, pane widths, corner radius, contrast, selection colour, unread styling, icon size and more. A live warning appears when your custom colours are hard to read.
• An optional colour per account, so it is always clear which account is active.
• Keyboard shortcuts with an in-app reference.

Gmail	Outlook (immersive)
Dracula (immersive, dark)	Windows XP (immersive, gradients)

More: dark theme · Roundcube Elastic

Mobile

The interface adapts to phones and tablets: a folder drawer, a full-screen reader and touch-friendly menus.

Message list	Reader (dark)

Security and privacy

• Mail server addresses are set by the administrator; users only enter their e-mail address and password.
• Protection against password guessing: per-mailbox and per-address lockouts with growing delays, applied before the mail server is contacted.
• Encrypted, revocable sessions with a list of active sessions and devices.
• Optional strict browser security headers.
• HTML mail is sanitised and shown in an isolated frame. Links open outside the preview, and remote content is blocked by default.
• Secrets are never shown in diagnostics.

Administration and deployment

• A single executable with the interface built in, a systemd service and Docker Compose examples.
• Databases: SQLite, MySQL/MariaDB or PostgreSQL. Sessions can also be kept in Redis.
• Attachment storage on local disk, a shared filesystem (NFS, CephFS, GlusterFS) or S3-compatible storage.
• Search with a built-in index or OpenSearch. A cluster mode runs several nodes behind a load balancer.
• Health and readiness endpoints, a diagnostics panel for users and an optional, protected diagnostics endpoint for administrators.
• Features can be switched on and off: filters, OpenPGP, multi-account, diagnostics, About page.
• A helper script imports contacts and identities from Roundcube.

See the README for configuration, Storage and search and System diagnostics.

Known limitations

• No CalDAV or CardDAV synchronisation yet. Calendar invitations cannot be answered from RustBox, and recurring events are stored but not expanded.
• No password-change integration and no IMAP shared-folder (ACL) management.
• Notifications work while RustBox is open in a browser tab.
• The current status of every area is tracked in Implementation status.