To carry on the last post, and yes another Mac bashing post, my scanner worked quickly and easily on Centos, another win for Centos! I then ran into a nasty Mail problem, the one where it uses up all memory because it tries to load gargantuan debug enabled log files on startup and zip them. This is described copiously on forums. In my case the log files are created by one IMAP mail account which constantly tries to update the mailbox into the 100,000s of messages, thus producing a 20G debug log file.
I thought initially this poblem was caused by GPGSuite (which did not initially work with El Capitan) so I removed it after copying that set of tools to Centos. However, it turned out not to be the problem so I put the latest GPGSuite back on the Mac.
In the meantime I had spent an hour or so with first line Apple Support who had no idea about the problem and simply ran through the standard troubleshooting steps.
As I’ve said before, the system has become so complex, I don’t think anyone understands it. Get back to simple!