[IOS-IMAP-016] Fix SwiftMail header encoding and MIME filename quoting upstream

[tabmail-kmyi]

Current status

Sync validation update: the proposed SwiftMail upstream pin is on hold after receive-path compatibility regressions were reproduced against the old app pin. The fork and app pin remain unchanged. The library's 619 passing tests do not establish app compatibility; resolve or adjudicate the regressions before synchronizing. The oversized-metadata train remains parked independently.

Updated 2026-09-09: upstream acceptance is complete. #215 was incorporated through #226, and #216 through #230, both merged September 7 with maintainer follow-ups. The latest published SwiftMail release is still 1.11.0, which predates them. Synchronization is blocked by reproduced receive-path compatibility regressions; this issue stays open and the current fork/app pins remain unchanged.

The separate oversized-metadata train (#74 / draft #103) remains parked for a SwiftNIO IMAP release containing #849 and subsequent SwiftMail adoption. That release dependency does not undo acceptance of this issue's header/MIME fixes.

Open. This issue tracks an upstream contribution to Cocoanetics/SwiftMail, followed by synchronization of TabMail's deviation-free SwiftMail fork.

TabMail should not carry a private fork-only remedy. The defects remain valid upstream even where TabMail has an app-side mitigation or a separately tracked app-owned surface.

The canonical technical record contains the current pin, reachability census, evidence, constraints, and related app-owned work:

• IOS-IMAP-016 canonical record

Original upstream scope (accepted; retained for reference)

• Correct SwiftMail's RFC 2047 header encoder so control-bearing values cannot be emitted literally.
• Bound encoded-words to the RFC 2047 75-octet ceiling without splitting invalid UTF-8.
• Correct all filename and content-type MIME parameter interpolation sites, with an upstream-compatible quoting/RFC 2231 policy.
• Add upstream regression tests for the full library surface, including sites not currently reached by TabMail.
• Submit the fix to Cocoanetics/SwiftMail rather than introducing a TabMail-only fork deviation.
• After upstream accepts and releases the remedy, synchronize TabMail's SwiftMail fork and update the app pin through the normal fork-sync workflow.

App-owned behavior and compatibility decisions remain tracked separately under IOS-COMPOSE-002 and IOS-COMPOSE-003; they do not replace the upstream library fix.

Completion criteria

• Upstream fix and regression tests are accepted by Cocoanetics/SwiftMail.
• A release containing the fix is available, or TabMail has an explicitly approved upstream commit to synchronize.
• TabMail's deviation-free fork is synchronized to that upstream state.
• The iOS app is re-pinned and its send/draft/render regression suites pass.
• The canonical IOS-IMAP-016 record is updated with upstream links, released commit/version, and verification evidence.
• Close this issue only after all of the above are complete; do not close it merely because an app-side mitigation exists.

Non-goals

• A permanent TabMail-only SwiftMail deviation.
• Closing the tracker as “not planned” solely because the work belongs upstream.
• Treating the app-side mitigations as proof that SwiftMail is fixed for other callers.

[tabmail-kmyi]

Re-triaged under the new P0–P5 priority scheme (2026-09-04): P4 → P3 — user-visible header/filename decoding defects with a readable fallback; fix upstream in SwiftMail, no fork deviation.

[tabmail-kmyi]

Status 2026-09-10:

• The app is re-pinned to the resynced fork: packages.SwiftMail.revision = d87295e3 via Decode RFC 2047 display names at the raw .eml boundary and pin the resynced SwiftMail fork #152 (merged). That revision is upstream 64a9a86 (which contains #226 and #230) plus the fork's one deviation, the RFC 2231 fix submitted as Read RFC 2231 continuations in one pass and honor every charset the platform names Cocoanetics/SwiftMail#233.
• #233 has been through four maintainer review rounds, all on the extended-parameter charset guard. Current head 9f1a2b6 is awaiting the maintainer. The three post-d87295e fixes change Apple-platform behaviour only for a blank charset with non-ASCII bytes, so the app pin is not blocked on them.
• Completion criteria 2–5 remain open: no upstream release or merged commit yet, and the fork still carries the deviation. Not closing. Record update in Record the SwiftMail #233 review rounds in the IOS-IMAP-016 status #156.

[tabmail-kmyi]

Update 2026-09-11: Cocoanetics/SwiftMail#233 was approved and merged upstream as 124e3cc. Fork main is reset to it and is a pure mirror again (no deviation). #156 re-pins app and NSE to 124e3cc, with the resolved checkout proven, app + NSE builds clean, and the EML/render consumer suites (175 tests) passing.

Completion criteria: (1) done; (2) satisfied by the approved upstream commit, though SwiftMail has no tagged release containing it yet (latest is still 1.11.0); (3) done; (4) done for the receive/render suites once #156 merges; (5) the canonical record is updated in #156. Remaining decision for the owner: close on the approved commit, or hold for a tagged release.