Scheduled send fails in Mail 5.8.0: `MimeMessage::build()` Argument #3 must be bool, array given

### Steps to reproduce

## Scheduled send fails in Mail 5.8.0: `MimeMessage::build()` Argument #3 must be bool, array given

### Summary

Scheduled sending does not work in Nextcloud Mail 5.8.0.

The global Nextcloud cron works correctly. The Mail `OutboxWorkerJob` is registered, runs normally, and executes after the scheduled send time. However, the scheduled message is not sent because `OutboxWorkerJob` fails with a `TypeError` in `MimeMessage::build()`.

Immediate/manual sending from the Mail UI works.

### Environment

- Nextcloud AIO
- Nextcloud AIO version: `13.0.4`
- Nextcloud version: `33.0.3`
- Mail app version: `5.8.0`
- Background jobs mode: `Cron`
- User timezone: `Europe/Bratislava`
- Server/container time: correct
- No Mail app update is currently available through OCC/App Store

### What I tested

The test message was scheduled for:

```text
21:55 CEST
```

UTC equivalent:

```text
19:55 UTC
```

The Mail outbox background job ran after the scheduled time:

```text
OCA\Mail\BackgroundJob\OutboxWorkerJob
Last executed: 2026-05-19T19:57:34+00:00
```

So the job clearly ran after the message should have been sent.

The message was a plain text test email without attachments.

### Mail background job exists and runs

```text
| 82495485209419777 | OCA\Mail\BackgroundJob\OutboxWorkerJob | 2026-05-19T19:57:34+00:00 | null |
```

Manual execution of the job also works:

```bash
sudo docker exec --user www-data -it nextcloud-aio-nextcloud php occ background-job:execute --force-execute 82495485209419777
```

Output:

```text
Job class:            OCA\Mail\BackgroundJob\OutboxWorkerJob
Arguments:            null
Type:                 timed

Forcing execution of the job

Job executed!
```

### Timezone checks

Host local time:

```text
Tue May 19 09:49:21 PM CEST 2026
```

Host UTC time:

```text
Tue May 19 07:49:21 PM UTC 2026
```

User timezone:

```text
Europe/Bratislava
```

Nextcloud system default timezone:

```text
Europe/Bratislava
```

The `OutboxWorkerJob` timestamp is in UTC and matches the expected CEST offset. This does not look like a timezone or cron scheduling issue.

### Error from `nextcloud.log`

At the time when the scheduled message should have been processed, this error appears:

```text
Could not send outbox message 101: OCA\Mail\Service\MimeMessage::build(): Argument #3 ($isPgpEncrypted) must be of type bool, array given, called in /var/www/html/custom_apps/mail/lib/Service/MailTransmission.php on line 138
```

Relevant part of the trace:

```text
OCA\Mail\Service\MimeMessage->build(
  "Skusobny email\n--\u00a0\u00a0\nTony Kraj\u010d\u00edk\n+421 949 731110\n\u00a0",
  null,
  [],
  false
)
```

The third argument passed to `MimeMessage::build()` is an array `[]`, but the method expects a boolean `$isPgpEncrypted`.

### Full relevant log entry

```json
{
  "level": 2,
  "time": "2026-05-19T19:57:34+00:00",
  "app": "mail",
  "scriptName": "occ",
  "message": "Could not send outbox message 101: OCA\\Mail\\Service\\MimeMessage::build(): Argument #3 ($isPgpEncrypted) must be of type bool, array given, called in /var/www/html/custom_apps/mail/lib/Service/MailTransmission.php on line 138",
  "version": "33.0.3.2",
  "occ_command": [
    "occ",
    "background-job:worker"
  ],
  "exception": {
    "Exception": "TypeError",
    "Message": "OCA\\Mail\\Service\\MimeMessage::build(): Argument #3 ($isPgpEncrypted) must be of type bool, array given, called in /var/www/html/custom_apps/mail/lib/Service/MailTransmission.php on line 138",
    "File": "/var/www/html/custom_apps/mail/lib/Service/MimeMessage.php",
    "Line": 35
  }
}
```

### Available Mail OCC commands

There does not seem to be a dedicated OCC command to repair or process the Mail outbox / scheduled-send queue.

```text
mail:account:create
mail:account:debug
mail:account:delete
mail:account:diagnose
mail:account:export
mail:account:export-threads
mail:account:sync
mail:account:train
mail:account:update
mail:clean-up
mail:repair:system-autoresponders
mail:repair:tags
mail:tags:migration-jobs
mail:thread
```

### Expected behavior

The scheduled email should be sent by `OCA\Mail\BackgroundJob\OutboxWorkerJob` after the scheduled time.

### Actual behavior

The scheduled email is not sent.

`OutboxWorkerJob` runs, but fails with:

```text
MimeMessage::build(): Argument #3 ($isPgpEncrypted) must be of type bool, array given
```

### Conclusion

This looks like a bug/regression in the scheduled send / outbox processing path in Nextcloud Mail 5.8.0.

The job runs correctly, but `MailTransmission.php` appears to call `MimeMessage::build()` with arguments in the wrong order or with the wrong type.

Immediate sending through the UI works, but scheduled sending through `OutboxWorkerJob` fails.

### Expected behavior

reported above

### Actual behavior

reported above

### Mail app version

5.8.0

### Nextcloud version

33.0.3

### Mailserver or service

_No response_

### Operating system

Nextcloud AIO - Ububtu server 24.0.4

### PHP engine version

None

### Nextcloud memory caching

_No response_

### Web server

None

### Database

None

### Additional info

_No response_

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Scheduled send fails in Mail 5.8.0: `MimeMessage::build()` Argument #3 must be bool, array given #12949

Steps to reproduce