Why are automation emails flagged as spam, some have bounced back and my email is blocked from sending any emails?

Issue
I set up a Custom Process to send a bulk email. The emails were flagged as spam, some bounced back and my email was blocked from sending any emails.

Cause
This has something to do with your Microsoft account.
Refer to this Microsoft article Remove blocked users from the Restricted users portal in Microsoft 365,
"If a user exceeds one of the outbound sending limits as specified in the service limits or in outbound spam policies, the user is restricted from sending email, but they can still receive email.

Solution
Contact your IT administrator to have this checked