I apparently updated postfix on May 10th to version 2.9.1-r2
My mail service stopped functioning.
Errors logged stated that /usr/lib64/postifx/(variety of different binaries) did not exist and, in fact, the directory,
/usr/lib64/postfix was absent.
Instead /usr/libexec/postfix contained the requisite binaries.
I added a symbolic link as follows:
ln -s /usr/libexec/postifix /usr/lib64/postfix
This restored functionality, but the true fix is elsewhere.