CreateMessage error when trying to add a message

Tried to copy a message from another account.

> CreateMessage (extractCachedData): message: malformed MIME header key:

Чек об оплате

```
So it announces itself like UTF-8 but actually it's UTF-8 displayed as Windows-1252 or so? Subject line is also malformed in a similar fashion. Also note the double `` tag.

No error in log files, this is only what Thunderbird displays and Thunderbird truncated the response.
### Log files
Log file is empty. (to clarify: completely empty with `debug 0` and no lines about this with `debug 1`)

### Server
maddy 0.6.2 linux/amd64 go1.18.3

```
storage.imapsql local_mailboxes {
driver postgres
}
```

------

I'd like to:
- get something useful in the log file about this
- actually receive this message in my inbox