The full list. The README carries a shorter one.
- Multiple accounts: IMAP, POP3 and JMAP, each on its own background worker, with a unified Inboxes view across all of them.
- JMAP: a Stalwart or Fastmail mailbox over the JSON mail protocol, including push. See Configuration.
- OAuth 2.0 sign-in: Google, Microsoft and custom providers over XOAUTH2. See Configuration.
- GNOME Online Accounts: import an account already set up in GNOME Settings, IMAP and SMTP accounts and Microsoft 365 over Graph included. See Configuration. Pausing an account's Mail service in GNOME Settings pauses it here.
- Per-alias SMTP: each address on an account can send through its own server and credentials.
- Proton Bridge, Zimbra, iCloud, Mailfence and other awkward servers: STARTTLS with locally signed certificates, a certificate in the hosting company's name rather than yours, servers without MOVE, and non-compliant fetch replies are all handled.
- Whole-mailbox sync and search: no message-count cap. A fast first page loads instantly; the rest indexes in the background with infinite scroll.
- Two-way sync: deletions, moves and flag changes from your phone or another client sync back automatically (IMAP IDLE plus reconciliation).
- Conversation threading, with the count covering the whole conversation across folders, not just the folder you are looking at.
- Moving mail between accounts: Move To lists every account's folders, and mail dragged onto another account's folder goes there too.
- Full folder management: create, rename, move and delete folders, assign the special roles (Drafts, Sent, Junk, Trash, Archive), and hide the ones you never open. An Exchange server's calendar, contacts and task folders are hidden from the start.
- Filters: multi-condition rules on sender, recipient, subject, body and Reply-To, with comma-separated alternatives; they tag mail, file it away, or both, and can be run over mail that is already in a folder.
- Tags: IMAP keywords, Graph categories, or a local fallback where the server has neither; custom colours, drag to reorder, and number-key shortcuts.
- Unified and filtered folders: Inboxes, Starred, Sent and Drafts across accounts, plus a folder per filter.
- Empty Trash and Junk, by hand or automatically after a number of days.
- Attachment gallery: every attachment in an account or folder in one place, with PDF first-page thumbnails, scoped by account and folder, and a deep archive scan that finds old attachments without downloading them.
- Printing: a message with its sender, recipients and date, with an in-app preview that also saves straight to PDF.
- Outbox: a send that fails is kept and retried when the connection returns, not lost. Queued messages can be edited, sent by hand or discarded.
- Send later: schedule a message for tomorrow morning, Monday, or any date and time; it waits in the Outbox, editable, until then.
- Four formats: rich text, Markdown, hand-written HTML, or plain text, switched per message from the composer's format button. See Writing in Markdown or HTML.
- HTML signatures, per account, with a default sender for new mail. In a reply or forward the signature sits above the quoted message, or below it if you prefer.
- Drafts that can be saved without a recipient, reopened inline, and deleted from the composer.
- Forwarding keeps the attachments: the original's files are attached to the forward, ready to send on. A reply does not repeat them.
- Inline images: dropped, pasted or picked from a file manager, resized by handle or menu, with an optional recompress on send.
- Spell check through the system dictionaries.
- Undo and redo across the whole message.
- Quote folding: a long quoted original folds away, interleaved replies intact.
- Split reply: answer one message of a conversation with the rest still on screen.
- Cloud attachments: upload a large file to your own Nextcloud, ownCloud, OpenCloud or Seafile server, or to OneDrive or Dropbox, and put a share link in the message, with an optional expiry and download password. See Cloud attachments.
- Send from Files: a Send with Hylki entry in the GNOME Files right-click menu sends the selected files into a new message, a draft or a reply of your choosing, with an offer to upload big ones to cloud storage instead. See Send with Hylki from GNOME Files.
- Privacy-first reading: remote content blocked by default, per-sender allow and block lists, and a per-message light/dark content theme.
- Reader View: one toggle shows every message in the conversation as its content alone: the sender's layout tables, colours, fonts, hidden preview text and tracking pixels are stripped, and what is left is set in one uniform sheet that follows the app's theme.
- Your own font and colours for message bodies, overriding the sender's.
- Message zoom: Ctrl++ and Ctrl+- scale the message alone, in Reader View or out of it, with the percentage shown beside the Reader View switch while it is away from the default. Settings → Reading sets the zoom every launch starts at; Ctrl+0, or a click on the chip, returns to it.
- Meeting invitations: what the meeting is, when it runs in your own clock and time zone, where it is and who organised it, with Accept, Maybe, Decline and Add to Calendar.
- One-click unsubscribe: a banner on list mail that leaves the list for you, by request or by email, without a browser where the list allows it.
- OpenPGP: read encrypted and signed mail, sign and encrypt what you send, and manage keys from Settings, through the GnuPG already on your computer. See OpenPGP.
- Sender identity: DKIM, SPF and DMARC checked on arrival, with BIMI logos where a domain publishes one.
- Message previews: the first one to three lines of each message under its subject in the list, or off.
- mid: links: a link to another message opens it (RFC 2392).
- GNOME-native: adaptive three-pane layout, per-account colours and emoji, picture or Gravatar avatars, light and dark following the system.
- Appearance themes: five palettes (Rose, Forest, Tidal, Earth and Midnight), each with its own light and dark version, or the stock GNOME colours.
- Focus Mode: Ctrl+Shift+F folds the toolbars, sidebar and list down to what you are reading, and puts it back afterwards.
- A customizable reader toolbar: reorder its buttons, or drag them in and out, in Settings → Appearance.
- Swipe actions on message rows, with an adjustable sensitivity.
- Single-key shortcuts: Gmail-style
j/k,r,a,dand friends, without a modifier. See Keyboard shortcuts. - Runs in the background (optional): closing the window keeps mail arriving; Hylki appears under Background Apps in the GNOME system menu, and can start at login without opening a window.
- Tray icon (optional): a StatusNotifierItem with a count of the folders you choose.
- Notifications that open the message they are about, with up to three buttons of your choice: Mark as Read, Archive, Delete, Reply, Forward or Mark as Spam.
- GNOME Contacts: names and photos from your address book, optional.
- Your language: the desktop's, or one you pick; a 12- or 24-hour clock following the desktop setting.