Send the read receipt the sender asked for

JMAP has an extension for this -- RFC 9007's MDN/send -- and Stalwart does
not implement it, so ihasmail assembles the RFC 8098 multipart/report itself
and sends it the long way round: raw MIME uploaded as a blob, imported,
submitted. That is also why the receipt lands in Sent, which is where it
honestly belongs.

The plumbing is the easy half. A receipt tells whoever asked that the address
is live and when the message was read, to an address the sender chose, so the
refusals are the feature: nothing marked Auto-Submitted (RFC 3834, or two
servers answer each other forever), nothing carrying Precedence bulk/list/junk
or a List-Id, nothing already acknowledged, nothing that never arrived. A
receipt aimed anywhere other than the sender is offered, but says so first.
There is no "always send" setting, only ask or never.

Sending is recorded with RFC 3503's $mdnsent keyword on the original rather
than remembered locally, so a second look -- or another client entirely --
knows not to ask again. Non-ASCII parts go base64 rather than 8bit, so
nothing rests on 8BITMIME surviving every hop.

Verified against the mock end to end: the blob uploads, the receipt imports
and submits, and the original reads back marked. Not yet exercised against
the live server.

README.md

@@ -49,6 +49,7 @@ seconds of downtime with nothing lost.
 - Safe HTML rendering: DOMPurify sanitisation inside a Shadow DOM, **remote images blocked by default** with a per-sender allow-list and an optional **privacy image proxy** (like Gmail's)
 - Messages sit on a light card by default, untouched as the sender designed them. *Appearance › Apply the theme to messages too* lets them follow the app's light/dark theme instead — plain-text mail always does, and with the option on so does HTML mail that brings no colours of its own; mail that styles itself is still left alone
 - Attachments: previews for images/PDF/text, download all, inline `cid:` images, `.eml` export, *Show original*, header viewer
+- **Read receipts**: when a sender asks for one, the message offers to send it — a real RFC 8098 `multipart/report`, never automatically. Bulk mail, mailing lists and anything marked `Auto-Submitted` are not offered one at all, and a receipt aimed somewhere other than the sender says so before you send it. Sending is recorded with RFC 3503's `$mdnsent` keyword, so a second look — or another client — knows not to ask again
 - Invitations: `.ics` parts render as an invite card with **Yes/Maybe/No** RSVP (via `CalendarEvent/parse` + iTIP); `.vcf` parts offer *Add to contacts*; `List-Unsubscribe` one-click
 - **Right-click anyone named in a message** — sender, To, Cc, Bcc, Reply-To — to add them to the address book (the contact editor opens prefilled, with the display name split into first/last), edit them if they are already known, write to them, or copy the address
 - Search with Gmail operators (`from:`, `to:`, `subject:`, `has:attachment`, `is:unread`, `is:starred`, `in:`, `label:`, `before:`, `after:`, `larger:`, `smaller:` …) plus an advanced-search panel
@@ -200,6 +201,7 @@ advertised the capability in the wrong place too, which is why nothing caught
 it. Fixed, and the mock now advertises it where the real server does — but
 the registry path is **awaiting live re-verification**.
 
+- **Read receipts are built here, not by the server** — JMAP has an extension for them, [RFC 9007](https://www.rfc-editor.org/rfc/rfc9007.html)'s `MDN/send`, and Stalwart does not implement it: `urn:ietf:params:jmap:mdn` is not among its capabilities. So ihasmail assembles the `multipart/report` itself and sends it the long way round — raw MIME uploaded as a blob, `Email/import`, then `EmailSubmission` — which is also why the receipt lands in Sent, where it honestly belongs. Non-ASCII parts are base64 rather than `8bit`, so nothing depends on 8BITMIME surviving every hop. There is deliberately no "always send" setting: a receipt confirms to whoever asked that the address is live and when it was read, to an address of the sender's choosing, so each one is a decision. Verified against the mock end to end (upload, import, submit, `$mdnsent`); **not yet exercised against the live server**.
 - **Where 0.16 advertises `urn:stalwart:jmap`** — not where a JMAP client would look. Stalwart builds the session-level `capabilities` from a fixed list (`Session::new`, plus WebSocket) that has never contained this capability, in any 0.16.x from 0.16.0 to 0.16.19. It hands it out per-account instead, so it appears in `primaryAccounts` and in each account's `accountCapabilities`. ihasmail tested for it in `capabilities` alone, which made every real 0.16 server read as pre-0.16 — and that one check drove three things: self-service credentials fell back to `POST /api/account/auth`, which 0.16 removed, so password changes, 2FA and app passwords all failed with "this mail server does not offer self-service credential management"; About reported the wrong generation; and Files took the pre-0.16 code path. It now looks in all three places. Two related soft spots went with it: a transport error while probing the registry no longer downgrades a server to the legacy REST path (which would have posted the current password to an endpoint that is not there), and a locale request that is merely refused no longer discards a generation the capability had already settled.
 - **HTML signatures** — Stalwart caps a signature at 2047 **bytes** (`value.len() < 2048` on a Rust string, so UTF-8 bytes, not characters). ihasmail compacts pasted HTML, moves images to Files and, if still too large, keeps the full signature in Files behind a short marker; other clients see a text fallback. Confirmed live on 0.15.5 (2026-08-24): oversized, non-ASCII and inline-image signatures all save, and a test message arrived intact at Gmail with the logo inline.
 - **Files on Stalwart before 0.16** — three things differ there, none of which the server reports as an error. (Confirmed live on 0.15.5 before the upgrade. The live instance now runs 0.16.19, where folder creation, upload, rename, move and delete are also confirmed; the older path is kept for anyone still on 0.15.x and covered by `npm run dev:mock:legacy`.) `FileNode/query` masks its results to non-containers, so it returns files and **never folders**; `nodeType` does not exist, and sending it fails the create outright (a directory is instead a node with no file properties at all); and rights are only `mayRead`/`mayWrite`/`mayShare`, so the finer-grained `mayDelete`/`mayRename` the UI gates on are absent. ihasmail detects the older server by the absence of `urn:stalwart:jmap` — looked for in `primaryAccounts` and `accountCapabilities` as well as the session capabilities, since that is where 0.16 actually advertises it — lists the tree through `FileNode/get` instead of query, shapes creates accordingly, and widens the old rights. Upload, folder creation, listing, rename, move and delete are all confirmed live on 0.15.5 (2026-08-24).
@@ -212,7 +214,7 @@ the registry path is **awaiting live re-verification**.
 ## Roadmap / not yet
 
 - Snooze (nothing in JMAP or Stalwart supports it, and ihasmail never stores a password, so nothing could act on a mailbox while you are away)
-- Read-receipt (MDN) sending, S/MIME / OpenPGP
+- S/MIME / OpenPGP
 - Translations (strings are English-only for now)
 
 ## License