What Does the Manual Status Mean?
If you have a flow email whose sending status is manual, emails will be queued, but not automatically sent. Setting a flow email to send manually is useful if you want to review who would receive the email or the content of the email if it contains dynamic content.
Instead of sending an email, if the person queued for a flow email meets the flow filters and would be sent an email, that recipient's status is marked as needing review. You can view recipients who need review by going to the Flows tab and clicking into a flow. If there are recipients that need review, they'll be visible to the right of each flow email.
Clicking on Needs Review will take you to a list of the recipients. You can individually preview, send and cancel each email. If you have a lot of recipients that need review, you can bulk send and cancel emails with the Send All and Cancel All buttons, respectfully.
When a flow email's sending status is updated from manual to live, recipients that need review are not automatically sent, you still need to review those emails.