When the mail spool server failed the other day, that machine also was one of the NIS slaves. I failed to take it out of the client mail server, mail.eskimo.com, yp.conf file and as a result at some point ypbind tried to rebind to a dead server.
During that interval, anyone who tried repeatedly to authenticate, and Macs and I-Phones do this automatically, got locked out by fail2ban for failed authentication attempts.
I discovered this today while trying to resolve a problem for my mother-in-law that also replicated on my tablet (but not the workstation that I use all day, go figure).
This has been corrected, all the banned IP’s unbanned. If anyone else is still having a problem contact me, 206-812-0051, and I will chase it down.