Mail not sending!

Hi,
Ironically whereas before the confirmation email was getting through and the notification wasn’t, since add the Ninja Mail service, now neither get through. As there is no configuration I don’t even know where to start. Test form submissions show up in the plugin log, but nothing in the https://my.ninjaforms.com log.

My client did the signing up so that they could pay, please give me a contact email so I can share their details privately to help identify them and resolve the issue.