Hello Seamus,
Please install the outlook IOS app from apple store which is the official app to send/receive emails for outlook.com emails addresses.
Below is the link that has the complete details on how to install and configure on IPhone.
https://support.office.com/en-us/article/set-up-office-apps-and-email-on-ios-devices-0402b37e-49c4-4419-a030-f34c2013041f?ui=en-US&rs=en-US&ad=US
Thanks and regards,
MSN Support Team