I recently updated my samba domain controllers (classic domain) from 3.6.25 to 4.4.7. Windows 7 and 2008 clients are OK. On Windows 10 , users were unable to login. The "max protocol" default had changed from "NT1" to "SMB3." Setting back to "NT1" fixed the issue (following a quick google search.) In the past Windows 7 and 2008 had issues with file shares with SMB2 (although authentication was not an issue.) This is a little counter-intuitive for me. If anything, I would have thought Windows 7 might have issues with SMB3 enabled on the DC and Windows 10 would be AOK. My guess is windows 10 tries SMB3 (if offered by the server) and chokes on it. SMB is primarily a file sharing protocol, not an authentication protocol, so I think that user authentication succeeded but that access to the IPC$ share failed. There don't seem to be any "server ipc protocol" options. This isn't really a major issue for now but I some point I would like to move samba file servers to smb2 or smb3 for the expected improved performance.