Exo Business is not compatible with "New" Microsoft Outlook
Exo Business uses the long supported MAPI (Mail API) to send emails.
The New Microsoft Outlook doesn’t support MAPI, so cannot be used to send emails.
We are considering alternatives at the moment. The only workarounds are to either
Do not use new Outlook. (Stay on Classic Outlook)
Use SMTP for mail, with BCC to sender email if you want to keep a copy of the email in Outlook