For infrequent small attachment use I would use 7zip with aes encryption. Also maybe ftp if you want a log of file access by user/IP and want to disable ftp accounts after a while.
I run my own ownCloud server. I also have a FTP server running but I've given up on that. I don't expect EU's to know how to use it but I do expect people in other IT service type companies know. That has not been the case the last few years.