opendkim error loading key
Solution 1:
The error message is quite clear "key data is not secure:" which indicates incorrect permissions on the key file, what is confirmed by the output of your ls command:
-rwxr-xr-- opendkim opendkim abcex.private
^
|__ world readable
Change the permissions for instance to:
chmod 0600 /etc/opendkim/keys/abcex.private
Solution 2:
In my case helped only this permission combination
chown -R opendkim:opendkim /etc/opendkim
chmod 0750 /etc/opendkim/keys
chmod 0600 /etc/opendkim/keys/abcex.private