Symptom
The sendmail process cannot start. The system.log file contains an entry similar to this:
sendmail[1195]: NOQUEUE: SYSERR(root): /etc/mail/sendmail.cf: line 93: fileclass: cannot open '/etc/mail/local-host-names': Group writable directory
Note: The Mail application does not require sendmail, which is turned off by default. If you don't know what sendmail is, you probably don't need it and should not be affected by this issue.
Solution
Sendmail requires alternate permissions for the root directory (/).
1. In Terminal, execute this command:
sudo chmod g-w /
2. Restart the computer.
Note: You may have to repeat these steps after installing software or repairing privileges on the startup volume.