Normally to enable postfix to start on boot on CentOS, you would run:

chkconfig postfix on

Though it sounds like you might be running into some other type of issue. Are you seeing any error messages when you try to start postfix manually with service postfix start?

Thank you for your reply. Tried running chkconfig postfix on w/ no luck. Service starts fine manually postfix start and all works well. I am just not having any luck getting it to start on server start.

I see the following in the mail.log however, when I check permissions on the directories postfix is the owner. I also ran set-permissions postfix with no luck

Jul 23 14:43:58 localhost postfix/postfix-script[1895]: warning: not owned by postfix: /var/spool/postfix/private/defer
Jul 23 14:43:58 localhost postfix/postfix-script[1896]: warning: not owned by postfix: /var/spool/postfix/private/proxywrite
Jul 23 14:43:58 localhost postfix/postfix-script[1897]: warning: not owned by postfix: /var/spool/postfix/private/smtp
Jul 23 14:43:58 localhost postfix/postfix-script[1898]: warning: not owned by postfix: /var/spool/postfix/private/local
Jul 23 14:43:58 localhost postfix/postfix-script[1899]: warning: not owned by postfix: /var/spool/postfix/private/verify
Jul 23 14:43:58 localhost postfix/postfix-script[1900]: warning: not owned by postfix: /var/spool/postfix/private/lmtp
Jul 23 14:43:58 localhost postfix/postfix-script[1901]: warning: not owned by postfix: /var/spool/postfix/private/relay
Jul 23 14:43:58 localhost postfix/postfix-script[1902]: warning: not owned by postfix: /var/spool/postfix/private/anvil
Jul 23 14:43:58 localhost postfix/postfix-script[1903]: warning: not owned by postfix: /var/spool/postfix/private/proxymap
Jul 23 14:43:58 localhost postfix/postfix-script[1904]: warning: not owned by postfix: /var/spool/postfix/private/tlsmgr
Jul 23 14:43:58 localhost postfix/postfix-script[1905]: warning: not owned by postfix: /var/spool/postfix/private/error
Jul 23 14:43:58 localhost postfix/postfix-script[1906]: warning: not owned by postfix: /var/spool/postfix/private/bounce
Jul 23 14:43:58 localhost postfix/postfix-script[1907]: warning: not owned by postfix: /var/spool/postfix/private/discard
Jul 23 14:43:58 localhost postfix/postfix-script[1908]: warning: not owned by postfix: /var/spool/postfix/private/trace
Jul 23 14:43:58 localhost postfix/postfix-script[1909]: warning: not owned by postfix: /var/spool/postfix/private/rewrite
Jul 23 14:43:58 localhost postfix/postfix-script[1910]: warning: not owned by postfix: /var/spool/postfix/private/virtual
Jul 23 14:43:58 localhost postfix/postfix-script[1911]: warning: not owned by postfix: /var/spool/postfix/private/scache
Jul 23 14:43:58 localhost postfix/postfix-script[1912]: warning: not owned by postfix: /var/spool/postfix/private/retry
Jul 23 14:43:58 localhost postfix/postfix-script[1913]: warning: not owned by postfix: /var/spool/postfix/public/pickup
Jul 23 14:43:58 localhost postfix/postfix-script[1914]: warning: not owned by postfix: /var/spool/postfix/public/cleanup
Jul 23 14:43:58 localhost postfix/postfix-script[1915]: warning: not owned by postfix: /var/spool/postfix/public/showq
Jul 23 14:43:58 localhost postfix/postfix-script[1916]: warning: not owned by postfix: /var/spool/postfix/public/qmgr
Jul 23 14:43:58 localhost postfix/postfix-script[1917]: warning: not owned by postfix: /var/spool/postfix/public/flush
Jul 23 14:43:58 localhost postfix/postfix-script[1926]: starting the Postfix mail system
Jul 23 14:43:58 localhost postfix/master[1927]: fatal: fifo_listen: remove public/pickup: Permission denied

Check iSElinux by command $sestatus
if SELinux status: enabled
then:
$restorecon -v -R /var/spool/postfix
restorecon reset /var/spool/postfix/pid/unix.cleanup context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixvarrunt:s0
restorecon reset /var/spool/postfix/pid/unix.local context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixvarrunt:s0
restorecon reset /var/spool/postfix/pid/inet.smtp context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixvarrunt:s0
restorecon reset /var/spool/postfix/private/tlsmgr context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/rewrite context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/bounce context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/defer context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/trace context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/verify context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/proxymap context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/proxywrite context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/smtp context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/relay context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/error context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/retry context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/discard context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/local context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/virtual context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/lmtp context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/anvil context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/private/scache context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixprivatet:s0
restorecon reset /var/spool/postfix/public/pickup context systemu:objectr:postfixspoolt:s0->systemu:objectr:postfixpublict:s0
restorecon reset /var/spool/postfix/public/cleanup context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixpublict:s0
restorecon reset /var/spool/postfix/public/qmgr context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixpublict:s0
restorecon reset /var/spool/postfix/public/flush context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixpublict:s0
restorecon reset /var/spool/postfix/public/showq context systemu:objectr:unlabeledt:s0->systemu:objectr:postfixpublict:s0
[root@lichsu ~]# systemctl start postfix

i have fixed my problem from 2 docs here:
https://linuxize.com/post/how-to-disable-selinux-on-centos-7/
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781776