"Delivery has failed to these recipients or groups" when sending emails in FYI

Issue
I can send emails directly from Outlook but when sending an email from within FYI I am getting the following error:

"Delivery has failed to these recipients or groups: email address
Your message wasn't delivered because the recipient's email provider rejected it."

Cause
This error can happen when you are trying out a Microsoft 365 trial tenant.

Solution
If you receive this error before you can purchase licenses, you will need to purchase a full Microsoft 365 license.
Refer also to the following Microsoft article https://docs.microsoft.com/en-us/Exchange/mail-flow-best-practices/non-delivery-reports-in-exchange-online/fix-error-code-5-7-700-through-5-7-750