Ok....now I just setup a plain proftpd from jessie (unpatched) and uploaded a big file (> 1 GB ...about 1.5 GB) without any problem via SFTP. FileZilla used here (on Ubuntu box is 3.7.3).
I have to check the versions in our "production", where the error occurs. There, FileZilla is used from a Windows machine (version number currently unknown). But trying with something else (e.g. WinSCP) also failed with some error. But additionally...I patched proftpd with the "large_file" patch (again taken from "unstable") and that also worked. SFTP is working normally (as far as I can tell). So...maybe there is also some other configuration that might trigger this problem. I'll try as soon as possible at the customer this problem arrised. Regards, Robert
