ulimit -n vs client_limit vs process_limit

[Joseph Tam]

As many of my users are accessing their mail remotely, I've seen
service loads increase and came across this log messages which I
haven't seen before

 	imap-login: Error: socketpair() failed: Too many open files: user=<*>, ...

I gather I have to increase file descriptor limits, which is currently
set to match

 	default_client_limit = 1000

What should I set "ulimit -n" relative to client_limit? Or perhaps I've roofed

 	service imap-login {
 		process_limit = 2
 		...
 	}

and should adjust that?

Joseph Tam <jtam.home at gmail.com>