As is described in the bat book, when you set:
O AliasFile=null:
no aliases will ever be found. However, if you put in your sendmail.mc:
define(`ALIAS_FILE’, `null:’)dnl
and the run sendmailconfig on a Debian Lenny, update_db will complain because it cannot handle the null: declaration. If you are bothered by this warning message, the solution is simple. Do not declare null: and instead:
# cp /dev/null /etc/mail/aliases
# newaliases
Managing organized complexity 