rssh is a Restricted Secure SHell that allow only the use of sftp

Port description for shells/rssh

rssh is a Restricted Secure SHell that allow only the use of sftp
or scp. It could be use when you need an account (and a valid
shell) in order to execute sftp or scp but when you don't want to
give the possibility to log in to this user.

you need to edit the config to allow sftp.

# vi /usr/local/etc/rssh.conf

uncomment following line:
allowsftp

# set the default umask
umask = 007