Emails sent to an outlook email address are returned with failed fraud detection
Welcome in the world of preventing spam. Your email is rejected by a Microsoft service, so Microsoft sets the rules. According to their documentation, the cause may be spoofing or, more likely in your case an incorrectly configured Sender Policy Framework (SPF) record.

You can reproduce this problem by sending a single email to an outlook address by using just the send mail action.

My assumption is that you sent your email directly from the server where CiviCRM is installed by using the mail() or the sendMail option in Settings - Outbound Mail . But your is not registered according to the SPF framework to be a legitimate email sender for your domain.

You can try to send the emails using SMTP server of your ISP (configure smtp in Outbound Mail). Another option is to add an SPF record to your DNS. More information at OpenSPF.

However, SPF is not the only countermeasure to discourage spam. The other is DKIM.

If you are sending large volumes of email you can consider using a specialised SMTP provider.