OCI: Postfix Fails to send Emails with "warning: /usr/lib/sendmail and /us/sbin/sendmail differ"

Applies to

Linux OS - Version Oracle Linux 7.0 and later

Oracle Cloud Infrastructure

Symptoms

 Postfix shows the following warning error:

Oct 13 07:23:55 <hostname> postfix/postfix-script[18461]: warning: /usr/lib/sendmail and /usr/sbin/sendmail differ
Oct 13 07:23:55 <hostname> postfix/postfix-script[18462]: warning: Replace one by a symbolic link to the other
Oct 13 07:23:55 <hostname> postfix/postfix-script[18463]: starting the Postfix mail system

 

In addition, when trying to send mail via cron the following message can be seen

Oct 13 07:30:01 <hostname> CROND[20069]: (oracle) CMDOUT (/usr/sbin/sendmail: Exec format error)

 

 Cause

 There were two issues here:

1) /etc/alternatives/mta-sendmail was pointing to /usr/lib/sendmail.sendmail instead of /usr/sbin/sendmail.postfix