Thanks - appreciate the info. Still, I would like to understand why these denials are occurring during what should be a pretty typical use case: namely sending emails from a web app. Does anyone have any insight into this?

If these denials do not interfere with the normal workflow of the application you may add dontaudit rules to your local policy. The unnecessary access will still be denied but you won't get these annoying messages in the logs.

There's a plenty of dontaudit rules in the base policy shipped with centos. If you're curious you may install /usr/share/selinux/targeted/enableaudit.pp which is a base policy with dontaudit rules turned off.