Postfix - master dead but pid file exists

Stop and start postfix. Do not restart, use individual commands for stop & start.

If you are still facing the problem
Remove /var/spool/postfix/pid/master.pid and /var/lock/subsys/postfix
Stop and start postfix

If you are still facing the problem, Check what is running on port 25

# netstat -lnp | grep :25

Kill the process and start postfix again.