Question 1

How to fix Apple Mail infinite IDLE loop with WildDuck IMAP server after EXPUNGE?

Accepted Answer

This is caused by WildDuck unnecessarily sending `* 0 EXISTS` after an EXPUNGE response, even when no messages were deleted, violating Apple Mail's expectations and triggering an infinite loop. The RFC does not require EXISTS after EXPUNGE.

To fix, modify the `onExpunge` handler in `lib/handlers/on-expunge.js` (around lines 139-150) to conditionally send `EXISTS` only when messages were actually removed:

```javascript
// Pseudo-patch: only send EXISTS if deletions occurred
if (deletedCount > 0) {
    // send EXISTS response
}
```

Apply the patch from the community fork (e.g., @titanism's fix) or manually wrap the EXISTS emission in a check for `deletedCount > 0`. Once patched, restart WildDuck. No official fix is available yet as the maintainer considers this an Apple Mail bug.

Question 2

Why does WildDuck throw a 'Cannot read property of undefined' error in updateMessage?

Accepted Answer

This occurs because the `updateMessage` function in WildDuck does not check if `options.session` exists before accessing it. The fix is to add a condition like `if (options.session && options.showExpunged)` before writing. A pull request (#843) has been submitted to address this. Update to a version of WildDuck that includes this patch, or manually apply the check in `lib/message-handler.js` around lines 2199–2201.

Question 3

How to fix "TypeError: connection._server.options.SNICallback is not a function" in WildDuck IMAP server?

Accepted Answer

This error occurs when starting an insecure IMAP server (e.g., on port 113) and a client like Apple Mail attempts STARTTLS. The internal IMAP core expects a valid `SNICallback` function on the server options even when not using TLS. To fix, always define `SNICallback` in your server options. For WildDuck, the callback is set automatically; if you're running a custom IMAP server using `wildduck/imap-core`, add:

```js
const tls = require('tls');

const server = new ImapServer({
  secure: false,
  SNICallback: (servername, cb) => {
    cb(null, tls.createSecureContext());
  }
});
```

This ensures the function exists. For WildDuck users, ensure you're on a version where the callback is always defined (≥1.42.5).

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