[Dovecot] Sieve-storage: couldn't find storage root directory

[Asai]

>> Using Dovecot 2.2.4.  In my DSync logs, I'm getting the error message:
>>
>> Error: sieve-storage: couldn't find storage root directory; sieve_dir was left unconfigured and autodetection failed
> What/how/where are you dsyncing?
>
>> However, I have the following configuration set:
>>
>> plugin {
>>   sieve = /vmail/%d/%n/sievescript
>>   sieve_dir = /vmail/%d/%n/
>> }
> Maybe the other side of dsync doesn't have it?
>
I am doing daily, weekly, and monthly backups of all maildirs to a 
backup server using this command:

dsync -u user at domain.tld backup maildir:/mnt/backups/<daily || weekly || 
monthly>/<domain>/<user>