Postfix fails with (error: postdrop: warning: mail_queue_enter: create file maildrop/randomfilename.xxxxx: Permission denied)

Problem: Postfix delivery fails with error

(postdrop: warning: mail_queue_enter: create file maildrop/randomfilename.xxxxx: Permission denied)


** see note below

Cause:

/usr/sbin/postdrop has incorrect permissions. 
Correct the permissions for /usr/sbin/postdrop are as follows:
# ll /usr/sbin/postdrop

-rwxr-sr-x. 1 root postdrop 180808 Aug 23  2018 /usr/sbin/postdrop

Solution:

Fix permissions with the following:

rpm --setperms postfix
rpm --setugids postfix

Source:
https://access.redhat.com/solutions/1592103

** Note: all of these steps were performed on a CentOS version 6. The same also applies to RHEL version 6

Further troubleshooting:

In order to prepare for this next part, you need to make sure that you have the yum-plugin-verify.noarch installed from your standard CentOS or RedHat YUM repository.

You can figure out the default permissions for whatever file that maybe having a permissions issue on your Linux system.

To prepare for this task, you need to make sure that you have the yum plugin
by doing the following:

• figure out which package provides the file you are troubleshooting.
• On my CentOS 6 system, this can be accomplished by running the command 
• rpm -q --whatprovides /usr/sbin/postdrop which will produce the following output indicating the package name that provided our postdrop file when it was installed:
• postfix-2.6.6-8.el6.x86_64
• Next step is to run the yum verify-all command against the package name to see the default ownership & permissions for its files as follows:
• yum verify-all postfix-2.6.6-8.el6.x86_64 
• The command above will produce something similar to the following output:

• Just please not that this screenshot is not indicative of the problem at hand because the permissions issues were fixed. This screenshot part is only complaining about checksums & mtime values since this postfix install was updated and modified multiple times.