I don't know FreeNAS, but is there really a directory called "//Disk-1/nUll/Backup" accessible if you were to login to like "ssh email@example.com". I doubt it. I suspect you want
# rsync -v -e ssh usr/ firstname.lastname@example.org:/Disk-1/nUll/Backup
# rsync -v -e ssh usr/ email@example.com
You may not need the "-e ssh" based on the config file.
[[ sorry that's a colon followed by one or zero slashes, not two slashes ]]