Contact-Form returning: Failed to send your message

Hello,

I’ve been trying to set-up the Contact Form in the Contact Page. By trying to send an Email from the Contact Form, I’m getting:
Failed to send your message. Please try later or contact the administrator by another method.

I’ve also took a look at wp_mail….which looks good, but don’t really know how to solve this.
I am not using the hoster’s email services but Office 365 from Microsoft.

Ticket