How can this happen?  It's getting denied, but not appearing in either the audit log or the messages file.  Running Centos 6 fully updated, php (drupal) inside of httpd tries to send mail via postfix (postdrop). 

When I have setenforce 0, the mail goes through.  No errors in any logs (audit.log, error_log, messages)

When I have setenforce 1, the mail gets blocked.  I get this message in httpd error_log:

                sendmail: fatal: execvp /usr/sbin/postdrop: Permission denied

sendmail: warning: command "/usr/sbin/postdrop -r" exited with status 1

sendmail: fatal: email@example.com(48): unable to execute /usr/sbin/postdrop -r: Success

I have auditd running.  In fact, I regularly use audit2allow to create allow policies on this machine.  So I can confidently say normally my selinux denials get logged in the audit.log.  I am at a loss to think of any reason this particular failure is not getting logged the same way my other error messages usually get logged.

I believe I can write a custom allow script by hand, but I believe I probably shouldn't, or if I try, it will fail for some reason. 

Thanks for your help...