E-mail and agenda for an iPhone/iPad

You can install your email and calendar on your iPhone via the Outlook app. 
To do so, download the Outlook app from the App Store and log in with your email address (firstname.surname [at] ru.nl).

Multi Factor Authentication (MFA) is required to set up your email.

Using Apple Mail

Alternatively, you can use Apple's mail and calendar app.
Note that not all features are supported.

Go to Settings > Passwords and accounts > New account > Exchange
Log in with your e-mail address (firstname.surname [at] ru.nl).

When prompted for a server address, enter outlook.office365.com.