# Known issues and pending QA

What was checked, against which server, and when. For a failure you are hitting
right now, start with [Troubleshooting](https://docs.ihasmail.org/troubleshooting/);
for what is not built yet, see [ROADMAP.md](ROADMAP.md).

The live instance runs **0.16.21**, and as of **2026-08-26 there is nothing
left pending**. Most entries below were exercised against 0.16.19 on the date
they name, and the dates still say so: each upgrade since was read against the
diff rather than re-run, and nothing in those diffs touches the session
capabilities, blob, quota, submission or registry paths these entries describe.
The calendar entries carrying a 2026-08-31 date were exercised against a live
0.16.20 directly, as were the public-key entries dated 2026-09-05.

**0.16.21 was different and was re-run rather than read.** It changed four
things a client can see, one of which resolved an entry below outright. The app
was run against a real 0.16.21 with mail, calendar and contacts exercised by
hand, including editing one occurrence of a recurring series through the
interface and confirming the rest of the series stayed where it was.
What remains here is not a list of unknowns but of things worth knowing — where
Stalwart departs from a spec, where a setting has to be turned on for a feature
to work, and what ihasmail deliberately does not do.

Entries keep saying what was checked and when, because this section has been
wrong before: the 0.16 registry path was once recorded as verified live when a
capability looked for in the wrong place meant it had never run at all.

Some entries record what a live **0.15.5** proved before that server was
upgraded on 2026-08-25. They are kept where the finding is about ihasmail
rather than about 0.15 — a byte cap that still applies, a flow that still
works the same way — and dropped where 0.15 was the whole subject. Support for
0.15 was removed on 2026-08-26; the last release that runs on it is tagged
[`stalwart-0.15-support`](https://github.com/Coffey-Labs/ihasmail/releases/tag/stalwart-0.15-support).

- **All nine translations have never been read by anybody who speaks them.** They were produced by AI against standard dictionaries on 2026-08-31 — German, Spanish, French, Dutch, Portuguese (Brazil), Russian, Ukrainian, Simplified Chinese and Japanese, which with English makes ten languages in the picker — and every one of the nine is marked **Beta** in the picker, with that stated in Settings beside a link for reporting anything that reads wrongly. This is the entry that matters most on this page, because it is the one thing here that cannot be closed by testing: a translation can be complete, consistent, pass every check, and still read like a machine wrote it, and nobody on this project can tell which. What *is* verified is the machinery around them. A missing key renders its English source, so a bad line can simply be deleted; a stale key — one whose English no longer exists — is caught by `npm run i18n:check` rather than sitting in the file looking correct and never being looked up. Plurals are asked of `Intl.PluralRules` rather than assumed, which is why Russian and Ukrainian carry three forms and Japanese and Chinese carry one; supplying `one` for Japanese would have been filling in a distinction the language does not draw. Confirmed live on the deployed instance (2026-08-31) against a 6,289-message mailbox: role folders localise and the ~20 custom folders keep the names their owner gave them, dates and the calendar follow the language, and 6,289 renders as *6289 листувань* — the genitive plural a number ending in nine takes, which is the first time the plural machinery ran on anything but a hand-picked value.

- **`npm run i18n:coverage` reported 100% while about two hundred strings rendered English in every language.** It reads JSX text, and it was not wrong about what it measured — none of them were JSX text. They were `toast.error(...)` arguments, `confirmDialog({ title, confirmLabel })` props, `title=` and `aria-label=` attributes, and template literals: every one built from an expression a codemod cannot read. The calendar's own view switcher was the clearest case, spelling its labels `v[0].toUpperCase() + v.slice(1)` — correct English, untranslatable anywhere else, and galling because **Day**, **Week**, **Month** and **Agenda** were already in all nine catalogues and the buttons simply never asked for them. Reported from production, where the switcher stayed English in a Japanese interface. All of them are now wrapped, and `npm run i18n:check` grew a second half (`scripts/i18n-literals.mjs`) that accepts a string wrapped where it is written *or* present as a catalogue key — the constant-table convention, where `SECTIONS` holds `label: "About"` and the render site calls `t(s.label)` — and refuses one that is neither, because that is a string no catalogue can translate however many languages ship. It found twenty more than a hand sweep had. Worth recording as a general lesson rather than an i18n one: a coverage number measures the thing it can see, and the strings it cannot see are exactly the ones nobody is checking.

- **A compressing hop in front of Stalwart truncated every blob download, and nothing said so.** Node decompresses a gzip response before the code ever sees the body, but leaves the `content-length` header describing the *compressed* bytes. The blob proxy copied that header onto the longer body it forwarded, so the browser stopped reading exactly that many bytes in and called the download complete. Reported on [#76](https://github.com/Coffey-Labs/ihasmail/issues/76) against a Coolify deployment, where Traefik's compress middleware only engages above 1 KiB: filter rules one and two were fine and the third pushed the script past the threshold, after which it came back cut off mid-rule — 384 bytes of a 1.3 KB script. The size threshold is what made it look like a race. This is the *second* cause behind that issue, and the first fix did not touch it: a truncated script is neither unknown nor empty, so the "refuse to save from a baseline we could not read" guard never fired — the script parsed, just with rules missing, and the next save wrote the short version back over the real one. Every blob download shared the fault, not just Sieve: message source, vCards, signature HTML, attachments being forwarded, and the `settings.json` sync. Settings degraded honestly by luck rather than design — a truncated file fails `JSON.parse`, which is caught and leaves the local cache in charge — so it stopped syncing between devices instead of being overwritten. The proxy now asks upstream for `identity` and, for a hop that compresses anyway, forwards no length at all rather than one describing different bytes. The image proxy is unaffected: it uses `node:http` directly, sends no `accept-encoding`, and never decompresses. The save path no longer trusts the transport either: a script is now checked for completeness against the shape the generator emits — every `# rule:` comment parses, every enabled rule has an `if` and a closed body below it, every block ends with a blank line — and saving refuses on anything short, as does the rule editor, which reports the script as unreadable rather than showing the rules that happened to parse. The check is structural rather than a re-serialize-and-compare, so a script written by an older version with a different serializer is still editable; refusing over a changed byte would be the worse bug. It catches a cut at every offset except the end of a complete rule block, which is a legitimately shorter script and indistinguishable from one in the bytes alone — that residual is what the proxy fix covers.

- **Delete all spam destroys, and does not pass through Deleted Items** — this is the point of the feature and the thing worth checking on a real server, since a folder that empties into another folder has solved nothing. `Email/set destroy`, walked a page at a time so it survives `maxObjectsInSet` the way emptying Deleted Items already had to. **Confirmed live on 0.16.19 (2026-08-26)**: Junk Mail emptied and Deleted Items stayed empty afterwards. There is no undo, which is why all three entry points share one dialog that says so. Only Deleted Items and Junk Mail can be emptied this way, enforced in the store rather than only hidden in the menus.
- **Sharing a mail folder is accepted and does nothing.** `Mailbox/set` with a `shareWith` map is applied, `Mailbox/get` reads it back, and the folder never appears for the account it was shared with — **confirmed live on 0.16.19 (2026-08-27)** with a folder shared read-only to another account on the same server, which never saw it. Stalwart's own sharing documentation lists calendars, address books and file storage; mail folders are not among them. Nothing reports a failure at any point, which is the whole problem: the share is stored, so a client that trusts what it reads back shows it as live for ever. The entry point is withdrawn. A folder that is *already* shared still offers **Stop sharing**, because a share nobody can see is exactly the one you want to be able to clear, and there is no other way to. File sharing is unaffected and works end to end.
- **Address book sharing works, and was briefly withdrawn by mistake.** It was taken out alongside mail folders on 2026-08-27 on a report that it behaved the same way; the report was mistaken and the feature was put back the same day. Nothing was ever shown to be wrong with it, and Stalwart documents address books as shareable. Recorded because the withdrawal is in the history and would otherwise read as a finding. Shared books now appear in the Contacts pane under "Shared with me" rather than behind an account switch, and their contacts are offered when addressing a message.
- **Stalwart lets a sharee subscribe to a shared calendar but not a shared address book.** Subscribing is a write to the *owner's* account -- `isSubscribed` lives on the collection, not on the reader -- and 0.16.19 refuses it for a book shared read-only: `AddressBook/set` answers successfully with the id in `notUpdated`, `forbidden`, *"You are not allowed to modify this address book."* The identical `Calendar/set` on a shared calendar is accepted. **Confirmed live on 0.16.19 (2026-08-27)** from a second account holding both shares, which is the only place it shows: from the owner's own account the write succeeds and everything looks fine. So ihasmail asks the server first, because a preference the server holds is one every client agrees about, and keeps the answer in its own synced settings (`addedShares`) when the server will not. Two things this cost, both worth remembering: the refusal arrives as a *successful* response, so the code that ignored `notUpdated` saw nothing wrong and the button simply did nothing; and it is invisible from the owner's account, so it took two browsers signed in as two accounts to find at all. The mock now refuses the same write for the same reason, since one that accepted it agreed with the belief that shipped.
- **`shareWith` is not returned unless a client asks for it by name.** A `Calendar/get` or `AddressBook/get` with no `properties` comes back without the field at all — not null, not empty, absent — **confirmed live on 0.16.19 (2026-08-27)** against a calendar and an address book that were genuinely shared with another account: omit the list and there is no `shareWith`; name it and the sharee is right there. Every consequence was silent. Nothing was badged as shared, "Stop sharing" never appeared because nothing looked shared, and the share dialog opened on *"not shared with anyone yet"* over a live share — so the one screen that existed to manage sharing was the one most confidently wrong about it. Files never had this, because `fileNodeProps` had always named the property; calendars, address books and mail folders fetched everything and got less. Mail folders mattered in a way of their own: sharing one is withdrawn, and the only way to clear a share already made is a **Stop sharing** entry that appears when a folder looks shared — so without the property the escape hatch for the exact situation it was built for was invisible. The mock now omits it the same way, since one that hands it over unasked lets a client that never asks look correct everywhere except against a real server.
- **Stalwart's `x:PublicKey` registry works, and ihasmail deliberately does not expose it.** A Settings section for it has been built twice — [PR #67](https://github.com/Coffey-Labs/ihasmail/pull/67), closed 2026-08-26, and [PR #285](https://github.com/Coffey-Labs/ihasmail/pull/285) — and withdrawn both times, for a reason that has nothing to do with the server: **nothing in ihasmail signs, encrypts, decrypts or verifies with a key**, so a page for managing them is furniture rather than a feature. It ends up telling the reader, in its own footnote, that adding a key does nothing. The registry is written up here rather than in [ROADMAP.md](ROADMAP.md) because what follows is established fact about Stalwart that cost a live probe, and losing it twice to a closed pull request was how the second attempt came to exist at all. Everything below was **confirmed live on 0.16.20 (2026-09-05)** from a normal account with no administrative rights, and the full round trip — create, read back, rename, patch, destroy — succeeded for both formats.

  - **An ordinary user may read *and* write their own keys**, whatever the permissions table says: Stalwart documents every `sysPublicKey*` permission as administrative, and the server granted them anyway. A create carrying a malformed key was refused with `invalidProperties` naming `key` rather than `forbidden` — a rejection of the key, not of the person. Had the documentation been right, any such feature would have been useless to everybody but an administrator, which is why this was probed first.
  - **It takes S/MIME certificates as well as OpenPGP keys, and parses both.** A self-signed X.509 certificate carrying `emailProtection` and an `email:` SAN registered, read back and destroyed cleanly, and a malformed one is refused by a decoder of its own: *"Failed to decode X509 certificate: BER decoding error: Expected Tag { class: Universal, value: 16 } tag…"*. Worth checking rather than assuming, because every *other* message the registry returns names OpenPGP — including for input that is not OpenPGP at all — so the server reads as though OpenPGP were the only format it knows. It is not.
  - **A key can parse perfectly and still be refused, and says something different when it is.** A sign-and-certify OpenPGP key with no encryption subkey — which is what `gpg --quick-generate-key` produces — comes back *"Could not find any suitable keys in OpenPGP public key"*, distinct from the parser's *"Failed to decode OpenPGP public key: Malformed packet: Malformed CTB…"*. Any client showing these must keep them apart: one says paste it again, the other says the key needs an encryption subkey and no amount of care with the clipboard will help. Certificates have no equivalent trap, since one issued for email use has key encipherment by construction.
  - **`emailAddresses` comes back as `{}` when empty** — an object, where a JMAP list property should be an array. Nothing fails loudly: it is a plain `Get` response that type-checks against a hand-written interface and then throws in `join()` while a list renders. A client must check the shape rather than trust the type.
  - **A create answers with the id alone**, no `createdAt`, so anything that reads the date back out of the create response gets `undefined`. **Patching `key` on an existing entry is allowed**, which is worth knowing and probably worth not doing: replacing a key by adding one and removing the old keeps `createdAt` meaning what it says.
  - **`expiresAt` is the registry's own field and is not derived from the key.** A certificate valid for a year registers with `expiresAt: null`. Reading the real date means parsing the certificate, and a date a client extracted would disagree with the server's field the moment the two ever differed.

- **Signature checking is done here, and its trust model is deliberately small.** Stalwart does not verify S/MIME or OpenPGP signatures and exposes no result for one, so ihasmail does it in the browser: raw message, MIME split, PKCS#7 parse, WebCrypto. What is worth knowing is what it does *not* do, because the gap is a design choice rather than an omission. **No chain of trust is validated** — a browser has no system trust store, no CA bundle is shipped, and revocation is not checked — so a verified signature on its own shows only that the sender held the key inside their own message, which anyone can self-sign. What carries the weight instead is trust on first use: the first signed message from an address pins its fingerprint in the account's settings, and a later message signed by a different certificate is reported loudly. That is why the interface never says the bare word "verified", why a first sighting is grey rather than green, and why a changed signer never overwrites the pin. Verified against real `openssl smime -sign` output rather than hand-built fixtures — RSA and ECDSA, plus a tampered copy — because a signed message written by hand only ever agrees with whatever the author believed the format to be.
- **OpenPGP signatures cannot be checked at all, for a reason that is not effort.** A PGP signature carries no key, so verifying one needs the sender's public key in advance, and there is nowhere to get it: `x:PublicKey` holds the *account's own* keys, not correspondents'. Fetching from a keyserver or via WKD would tell a third party who you correspond with each time you opened a message — the same leak the image proxy exists to close — so it is not done. Such a message says so by name rather than failing as an unknown format, and it says *could not check* rather than *did not check out*, which is a distinction worth keeping: one is ignorance and the other is an accusation.
- **Two signature shapes are declined rather than attempted.** SHA-1 signatures are refused outright — one nobody can forge in practice today is still not one to put a tick beside. RSA-PSS is declined because the salt length lives in parameters ihasmail does not read, and guessing wrong would report a perfectly good signature as *bad*, which is a far worse thing to say than "cannot check". Both are shown as uncheckable, not as broken.
- **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, `$mdnsent`), and **confirmed live on 0.16.19 (2026-08-26)**: a receipt asked for by a real sender was assembled, uploaded, imported and submitted, landed in Sent, and set `$mdnsent` so a second look does not offer to send another.
- **Where 0.16 advertises `urn:stalwart:jmap`** — not where a JMAP client would look, and this now decides whether a sign-in is allowed at all. 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 older than 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 older code path. It now looks in all three places, and is covered by tests on each. Worth restating plainly, because the stakes went up when 0.15 support was dropped: there is no longer a fallback path for this check to be wrong *into*. Getting it wrong now refuses every sign-in against a perfectly good server — a loud failure rather than a quiet misrouting, which is the trade the removal was making.
- **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.
- **Settings live in the account's Files, not the browser** — every preference used to sit in `localStorage`, so none of them followed anyone between devices. The sharpest edge was the default identity: with none set the address that sorts first wins, so someone who set it at work found it unset at home and mail went out from an address the recipient might not recognise ([#54](https://github.com/Coffey-Labs/ihasmail/issues/54)). They are now a `settings.json` in the `ihasmail` folder in JMAP Files, beside the signature images already kept there — which keeps ihasmail itself stateless: no volume, no database, nothing to back up separately, and the settings are covered by whatever backs up the mail store. `x:AccountSettings` was the other candidate and does not fit; its schema is `locale`/`timeZone`/`description` with no free-form field, and writing it needs `sysAccountSettingsSet`, where the built-in user role carries only the `…Get` half. `localStorage` stays on as a *cache* rather than the source of truth, so the first frame paints from it and the file corrects it a moment later; a browser with no cache shows defaults for that one frame, which is the trade for not gating the whole app on a round trip. Settings that describe *this* screen or browser deliberately stay local — list-pane sizes, density, font size, sidebar state, and the notification toggles, which track a permission the browser grants per-device and would be a claim about somewhere else it cannot make. That split is written as a list of exceptions, so a setting added later syncs by default. Writes are coalesced behind a three-second debounce, since `update()` fires on every frame of a splitter drag, and a tab going away or a sign-out flushes first. The `ihasmail` folder is now hidden from the Files view, contents and all: hiding the folder alone would be worse than showing it, because the tree attaches a node whose parent is missing to the root, so the signature images — visible there since signatures shipped — would have spilled into the top level. **Confirmed live on 0.16.19 (2026-08-26)**: settings set in Chrome came back on a fresh login in Firefox and in an incognito session, both of which start with an empty cache, so each read the account's file rather than anything local. Confirmed again on the deployed instance rather than only a pre-deployment build. Requires 0.16, which ihasmail now requires everywhere — `FileNode/query` cannot see directories before that, and sign-in refuses an older server outright. Two limits worth knowing: conflicts are last-write-wins, and a change made on one device does not reach another that already has ihasmail open until it signs in again.
- **Files on 0.16** — the pre-0.16 quirks this entry used to describe are gone with the support for them: `FileNode/query` masking directories out of its own results, `nodeType` not existing, and rights being a single `mayWrite`. What is left is what has actually been exercised on 0.16.19. Finding and creating a folder, creating a node with `nodeType`, uploading and downloading its blob, and pointing an existing node at a new one all ran live on 2026-08-26, as a side effect of the settings file. Rename, move and delete are **confirmed live on 0.16.19 (2026-08-26)** as well, which closes this out: what had been confirmed on 0.15.5 (2026-08-24) was the older code path, and that path no longer exists. Two fallbacks went with the removal and are worth knowing about: `ensureFolder` and `findInFolder` now filter on `parentId`/`isTopLevel` alone and match names client-side, since `name` is not a filter Stalwart is known to implement and one it does not know fails the whole query; and a refused filter or sort no longer drops the view into fetching every node in the account, which would have hidden a real fault behind a performance cliff nobody would notice.
- **Self-service credentials** — the registry path is **confirmed live** against Stalwart 0.16.19 (2026-08-25): app passwords created and revoked, password changed, 2FA enabled and disabled, with the browser session surviving the switch to an app password. The 0.15 REST path was confirmed live too, on 0.15.5 (2026-08-24), and has since been removed along with the rest of 0.15 support. The mock enforces the same rules the real server does (current password required, password policy, a TOTP code on every request once 2FA is on, app passwords exempt from it). Password changes are refused by Stalwart for accounts backed by an external directory (LDAP/SQL/OIDC); the server's own message is shown when that happens.
- **Scheduled send needs one setting turned on, and says nothing when it is off.** Stalwart advertises the delay in the account's `urn:ietf:params:jmap:submission` capability — `maxDelayedSend: 2592000` (30 days) and `FUTURERELEASE` among its `submissionExtensions`, and note it is the *account* capability, not the session-level one, which is empty. But the MTA only honours a hold when `futureRelease` is set under the session's MTA extensions, and [that setting defaults to `false`](https://stalw.art/docs/ref/object/mta-extensions/). With it off, Stalwart takes the `HOLDUNTIL` parameter, skips the hold and sends the message immediately **without an error** — the capability still says thirty days. So set `futureRelease` (to the longest hold you want to allow) before relying on this; a value shorter than 30 days is fine, and a request past it is refused honestly, with a `forbiddenMailFrom` naming the limit. `npm run dev:mock:no-future-release` reproduces the silent-drop case. ihasmail asks for the delay the way JMAP requires — a `HOLDUNTIL` parameter on the envelope's `mailFrom`, since RFC 8621 makes `sendAt` read-only and server-derived — and files the held message in a **Scheduled** folder, because `onSuccessUpdateEmail` would otherwise drop it in Sent the moment the submission is created. Nothing moves it out when the hold expires, so ihasmail reconciles the folder on the way in: released messages to Sent, cancelled ones back to Drafts. Three fixes this depends on landed in **0.16.17**, below the live instance's 0.16.19: `HOLDUNTIL` taking RFC 3339 date-times again (0.16.16 had it wanting Unix timestamps), `EmailSubmission/query` on `undoStatus` agreeing with `/get` about held submissions, and `EmailSubmission/get` without `ids` iterating the right index. The hold itself is now **confirmed against the live 0.16.19** (2026-08-25), once `futureRelease` was set to `30d` there: a submission carrying a `HOLDUNTIL` ten minutes out came back `pending`, with `sendAt` equal to the time asked for and a `250 2.1.5 Queued` from the MTA, rather than going out at once. Worth repeating that the capability is no evidence either way — it advertised `maxDelayedSend: 2592000` and `FUTURERELEASE` while the setting was still off. Only a submission tells you. The rest of the journey is **confirmed live too (2026-08-26)**: a hold expired and was delivered, and the **Scheduled** folder reconciled on the way in — a released message moved to Sent, a cancelled one back to Drafts. Nothing in Stalwart does that moving, so if ihasmail is never opened again the message still goes out; it is only the folder that waits to be tidied.
- **Stalwart 0.16 and RFC 8984 disagree about the calendar vocabulary, and the server only says so half the time.** A participant's address lives in `calendarAddress`, not RFC 8984's `sendTo`/`email`; the organizer is `organizerCalendarAddress`, not `replyTo`; and a recurrence is a single `recurrenceRule`, not a `recurrenceRules` array. Addressed the RFC's way, `CalendarEvent/set` **keeps the event and discards the whole participant map without an error** — guests disappeared on save and no invitation was ever sent, which is what [#26](https://github.com/Coffey-Labs/ihasmail/issues/26) reported. The array form of the rule is refused honestly, with `invalidProperties`, so recurring events could not be created at all and existing ones showed no repeat ([#30](https://github.com/Coffey-Labs/ihasmail/issues/30)). ihasmail now writes Stalwart's names and reads either, and the mock refuses what the real server refuses, since advertising the RFC spelling is precisely how this got as far as a live server. Verified against 0.16.19 on 2026-08-25, end to end: participants, organizer and rule all survive a create, an update and a re-read; an invitation to an external Gmail address arrived as an invite card, and the decline came back and was applied to the event (`needs-action` → `declined`, sequence 1). Cancelling the event notified the guest too. Adding guests to an event that had none, and clearing them again with `null`, both work on the update path, as does RSVP — which patches `participants/{key}/participationStatus` (and `participationComment`) rather than sending the whole map. That patch had to be aimed at the base event: through 0.16.19 `CalendarEvent/set` refused a synthetic id with *"Updating synthetic ids is not yet supported"*, which is why RSVP resolves `baseEventId` first. 0.16.20 accepts one, so that resolution is now a choice rather than the only option — an RSVP aimed at an occurrence would answer for that date alone. It still resolves the base, which is the answer people mean. Adding a *new* participant by patch is refused as well (`Patch operation failed`), so a changed guest list is written as the whole `participants` property. One more thing to know when reading this code: an expanded occurrence carries a `recurrenceId` but *no* rule of its own, and `baseEventId` is set on everything an expanded query returns — a one-off included, whose own id differs from its base — so neither is a test for recurrence.
- **Free/busy between accounts needs no sharing, and calendar contents cannot be reached at all.** These are the two halves of the same finding, and the second is what makes the first safe. **Confirmed live on 0.16.20 (2026-09-01)** against the deployed instance: `Principal/getAvailability` was called for all seven principals the directory returns, none of whose calendars are shared with the calling account, and every one was answered — no `forbidden`, no error of any kind, from a server that refuses a malformed call instantly. It returns real data rather than a polite empty list: the caller's own principal reported one busy period against the one event in the next sixty days. And a `Principal` carries only `id`, `type`, `name`, `description` and `email` — **no `accountId`** — so there is no handle with which to ask for anybody's calendars. Free/busy is therefore not the weaker of two permissions, it is the only channel between two accounts, and it is open by default. That is the right posture and worth recording, because a client that assumed sharing was a precondition would hide a working feature behind a setting nobody needs to touch. **One thing this did not settle**: the other six principals reported nothing over a nine-month window, which is equally consistent with "those accounts have empty calendars" — likely, since the session reaches one account — and with "an unreadable principal answers with an empty list rather than an error". Distinguishing them needs a second account with an event in it, and until somebody has one, ihasmail assumes the pessimistic reading everywhere it matters: a participant it cannot read is drawn as unknown rather than as free.

- **An override can move an occurrence, and then `start` and `recurrenceId` mean two different times.** The slot stays where the rule put it and only the clock time moves. **Confirmed live on 0.16.20 (2026-08-31)**: one occurrence of a weekly 09:00 series moved to 14:00 came back `start: 2027-06-14T14:00:00` with `recurrenceId` still `2027-06-14T09:00:00`. This is the right behaviour and it is the reason `recurrenceId` is the handle ihasmail holds: it is the one name for an instance that survives *both* a renumbering and a move, so a mutation can always be re-resolved from it. Worth recording because the mock got it wrong in the other direction — it overwrote an override's `start` with the slot time, so a moved occurrence did not move, and per-occurrence *time* editing looked broken against the mock and correct against the server. Found by asking a real server rather than by reading the mock, which is the only way this kind of disagreement ever surfaces.

- **A synthetic id was only true until the next write, through 0.16.20. Fixed in 0.16.21.** Stalwart's expanded-occurrence ids used to encode a position in the series, so writing a `recurrenceOverrides` entry renumbered them. **Confirmed live on 0.16.20 (2026-08-31)**: a five-week series came back as `e i m q u` over 03-01 … 03-29; one override written to 03-08 left the *same five ids* addressing 03-01, 03-15, 03-29, 03-08 and 03-22. Nothing was rejected and nothing reported a change — `i` simply meant a week later than it had a moment earlier, so an id cached across a write silently pointed at another date and a delete meant for one occurrence removed a different one. The failure was never a `notFound` a client would notice; it was a confident answer about the wrong day. **0.16.21 identifies an occurrence by its recurrence id, and confirming that was the point of re-running rather than reading the diff. Confirmed live on 0.16.21 (2026-09-06)**: the same shape of test — five weekly occurrences expanded, the third retitled through its own synthetic id, all five original ids re-read — left every id on its own date, with none renumbered and none `notFound`. A second override written through the interface behaved the same way. The defence stays regardless: ihasmail still never mutates an occurrence by an id it is holding, and `updateEvent` and `destroyEvent` still re-resolve by `recurrenceId` immediately before acting, because a date can still leave a series and because the client supports 0.16 as a whole rather than only its newest release. The mock follows the new behaviour, and the test that pinned the old renumbering now pins the stability instead — rewritten rather than deleted, so the reversal stays on the record.

- **A per-occurrence patch made only of inherited properties creates an override that loses the title.** The twelve properties 0.16.20 drops from a per-occurrence patch are dropped *after* it has decided to write an override, so a patch consisting only of them still writes one — and that override carries the `start` and `duration` the server fills in and nothing else. **Confirmed live on 0.16.20 (2026-08-31)**: `{"privacy": "private"}` aimed at one occurrence answered `updated`, left `privacy` untouched on the series, and left that date with no title at all. A successful response, a silently discarded change, and real data loss on a third property nobody mentioned. ihasmail narrows a per-occurrence patch before sending it and sends nothing when narrowing empties it, which was written as a point of principle — a request whose response could only be a meaningless "updated" is worse than no request — and turns out to prevent this. Worth remembering as the argument for the principle.

- **Recurring events can be edited and deleted one date at a time, since 0.16.20.** A write aimed at a synthetic id was refused outright through 0.16.19; 0.16.20 turns it into a `recurrenceOverrides` entry instead, so "this occurrence" and "the whole series" are now two different things ihasmail asks about before acting. **Confirmed live on 0.16.20 (2026-08-31)** end to end against a five-week series: a legal patch landed on the override with `start` and `duration` filled in by the server; `useDefaultAlerts` was refused with *"This property cannot be modified on a single occurrence."*; a destroy removed one date and left the series; and a base event and one of its instances in the same request were refused together, both ids, with *"A base event and its instances cannot be modified in the same request."* The scope is chosen before the editor opens rather than on save, because it decides which event the form is about — one populated from the master shows the *series'* start date, so editing Wednesday would have offered to move Monday. Two entries below are the sharp edges this turned up.
- Editable date boxes are always Gregorian and in Latin digits, even for locales whose *display* uses another calendar or numbering system (`fa-IR`, `th-TH`, `ar-EG`) — they keep the locale's field order and separator, but a Buddhist-era year in a text box does not round-trip against the Gregorian calendar grid. Non-Gregorian calendar support is not implemented.
- The account locale is read from `x:AccountSettings/get`, whose permission the built-in user role has, falling back to `x:Account/get` (which needs the admin-only `sysAccountGet`). Both are Stalwart 0.16 methods: **on older servers neither is reachable** — they do not implement the registry and reject a request that so much as names the `urn:stalwart:jmap` capability — so there the locale still falls back to the browser's and can be chosen by hand. Confirmed live on 0.16.19 (2026-08-25), once the capability was looked for where Stalwart advertises it; a locale request that is merely refused no longer downgrades the detected generation.