You are troubleshooting a FortiMail Cloud service integrated with Office 365 where outgoing emails are...

A. The FortiMail access control rule to relay from Office 365 servers FQDN is missing.

If the access control rule to relay from Office 365 servers FQDN is missing, then FortiMail will not be able to send emails to Office 365. This is because the access control rule specifies which IP addresses or domains are allowed to relay emails through FortiMail.

D. A Mail Flow connector from the Exchange Admin Center has not been set properly to the FortiMail Cloud FQDN.

If the Mail Flow connector from the Exchange Admin Center is not set properly to the FortiMail Cloud FQDN, then Office 365 will not be able to send emails to FortiMail. This is because the Mail Flow connector specifies which SMTP server is used to send emails to external recipients.