If you can't send mail because the postfix mail server is stopped, then the best thing to do is find out why it won't start. A good command to run is this:
# postfix start
If you see an error like this:
postfix: fatal: config variable inet_interfaces: host not found: localhost
you can change the inet_interfaces setting in /etc/postfix/main.cf from:
inet_interfaces = localhost
inet_interfaces = 127.0.0.1
and postfix should start right up.