You may experience mailbox locking problems, signified by these error messages:
mail: Cannot read lock file '/usr/spool/mail/username'
Or, if mail is delivered to $HOME/.mailbox, the message is
mail: Cannot read lock file 'username/.mailbox'
10/ 5 10:15:06 local 0913: [SYSERR (13) Permission denied] open of /usr/spool/mail/root
10/ 5 10:15:06 local 0913: [SYSERR (13) Permission denied] can't open mailbox '/usr/spool/mail/root'
The MLCKTYPE parameter is useful if the users on the system use third party mail user agents (MUAs) that use a lock file that is different from the standard System V lock file.
This mailbox locking problem occurs when MMDF fails to unlink the /usr/spool/mail/username.lock or /tmp/username.mlk file, which is created to lock the mailbox. If mail is delivered to $HOME/.mailbox, the lock file is /tmp/.mailbox.lock. A subsequent fcntl(M) (kernel file locking) process returns with a permission denied error because it cannot lock the mailbox.
To resolve the locking problem, log in as root and enter this
at the root prompt: