Here's the update. As a summary, this change:

2. changed the call to `open-network-stream' in the patch above to
>> @@ -244,8 +267,7 @@ sieve-manage-open-server
>>                   (open-network-stream
>>                    "SIEVE" buffer server port
>>                    :type stream
>> -                  ;; eol type unix is required to preserve "\r\n"
>> -                  :coding 'raw-text-unix
>> +                  :coding sieve-manage--coding-system

needed to be reverted to what I had earlier:

>> @@ -244,8 +267,7 @@ sieve-manage-open-server
>>                   (open-network-stream
>>                    "SIEVE" buffer server port
>>                    :type stream
>> -                  ;; eol type unix is required to preserve "\r\n"
>> -                  :coding 'raw-text-unix
>> +                  :coding `(binary . ,sieve-manage--coding-system)

I updated the text below and the patches accordingly.





Hello Eli,

thanks for looking into this! 

Eli Zaretskii <eliz@gnu.org> writes:
> The duplicate use of with-current-buffer is sub-optimal,
> IMO.  What about the simpler code below:
>
>   (when sieve-manage-log
>     (let* ((existing-log-buffer (get-buffer sieve-manage-log))
>            (log-buffer (or existing-log-buffer
>                            (get-buffer-create sieve-manage-log))))
>       (with-current-buffer log-buffer
>         (unless existing-log-buffer
>           ;; Do this only once, when creating the log buffer.
>           (set-buffer-multibyte nil)
>           (buffer-disable-undo))
>         (goto-char (point-max))
>         (apply #'insert args)))))

Yes, that provides more insight into what the code intends to do. Here's
the patch (with additional updated doc string):