Just built sendmail 8.12.4-r3 on PPC and x86 and both cannot send out mails without me changing manually the permissions in /var/spool/clientmqueue to rwxrwxr-x from the previous rwxr-xr-x Since the user smmsp needs write access to this directory, I don't understand why it does not work out-of-the-box. Sendmail warns afterwards that the permissions 40775 are dangerous. Maybe setting the SGID instead of the SUID is less dangerous.
Should be fixed now.
Broken again in 8.12.10 through 8.12.11 (at least).