hello
i just install auto_backup and i made pip install pysftp. It was the 2.9 version.
i can not connect to external storage with pysftp due to error: SSHException: No hostkey for host XXXX
after search around it seems due to update of pysftp
Change Log
0.2.9 (current, released 2016-07-04)
bugfix: correctly implement hostcheck. Now, be default pysftp will verify the host. See pysftp.CnOpts.hostkeys
added pysftp.Connection.remote_server_key - used to retrieve the remote hosts server key.

so i resolve my issue with
pip install pysftp==0.2.8

maybe we need to add destination storage public host key somewhere ?
regards