Send "Email Broadcast" using Automation Flow
This is a nice easy one, and you'll kick yourself once you realize how easy it is.
Go to the flow builder.
Don't add a trigger.
Drag "Send Email" onto the flow canvas.
Set up the email with "Sender", "Subject" and the email body etc.
Publish the flow and call it "Email Broadcast".
Now just go to the Contacts/Database page, select who you want the email broadcast to go to and "Add to Automation".
Et voila!
Please be aware your email broadcast will have a rate limit set by your SMTP provider. If you're sending to large lists in the tens of thousands or more, they won't send every email instantly.