Good day, I was checking my syslog this morning and I ran into this error:
Apr 26 06:42:50 postfix/postfix-script: warning: /var/spool/postfix/etc/localtime and /etc/localtime differ
Apr 26 06:42:50 postfix/postfix-script: warning: /var/spool/postfix/etc/hosts and /etc/hosts differ
Apr 26 06:42:50 postfix/postfix-script: warning: /var/spool/postfix/etc/host.conf and /etc/host.conf differ
Apr 26 06:42:50 postfix/postfix-script: warning: /var/spool/postfix/etc/resolv.conf and /etc/resolv.conf differ

I didn't know there was a hosts file in directory /var/spool/postfix/etc/
It is in fact different. This is my etc/hosts file:
xxx.xxx.x.x domainname alias
127.0.0.1 localhost
This is my /var/spool/postfix/etc/hosts file:

127.0.0.1 localhost.localdomain localhost

Just another fork in the road. Asking questions really makes me understand the Linux system more clearly. Thanks.