Notification Mailer show status system deactivated

We are using EBS version 12.1.3

For our production instance, not sure why, but the notification mailer all of a sudden shows system deactived status. What would cause this to happen? Is there a log file somewhere that I can check?

I restarted the notification mailer and now people are able to receive emails again. But the OAM page shows notification mailer, agent listener, service components, background engines, control queue cleanup as green check, however, purge is red x as down. Why is this? How often should the purge be run? Please advise. Thank you very much.

I am still relatively new to EBS. Thanks.