I was getting the following error from sendmail after upgrading from Fedora 14 to Fedora 15 (x86_64):
Milter (greylist): local socket name /var/run/milter-greylist/milter-greylist.sock unsafe
Milter (greylist): to error state
After a couple of hours, and much hunting on the internet, I realised that it was not a standard answer (i.e.: permissions, etc). Instead the daemon had not been started. Apparently sendmail has been moved to the new systemd (systemctl) and greylist was still using (only) upstart. So the daemon was not starting when sendmail would be kicked off. I created an sysv init script to kick it off and everything works.
Side note: Fedora please don't switch init systems *again*. If anyone wants to create a systemd init script for it I would love it!
I have to relearn the init process and am too busy at the moment.