Email notification on pull requests

Hi,
We have our travis CI running inside a private network and so is git.

I am seeing that currently we are not receiving email notifications even though we have configured to receive email notifications. I have verified that the email address on git is verified and we sign in with github. And we use build stages which is a beta feature to run our tests. Also we have configured Travis to kick off only on creation of a PR.

Any pointers to help troubleshoot why we are not receiving emails.
email:
on_failure: always
on_success: never

If this is an Enterprise installation, please email us at support@travis-ci.com. There should be logs that can help you (or your Travis administrators) troubleshoot it.