how to? when I make new post people receive the post (not just a notification) via email

Is this built in to Wordpress? If not, can someone point me to a plugin please? The WPMUdev 'subscribe' plugin doesn't seem to exactly do it.

Requirements:
1. when I post, people receive the post in an email
2. I can import my list of existing users (nice but not mandatory)
3. people can choose to 'subscribe' or 'unsubscribe' (or signup or join list or whatever you want to call it)
4. people can choose whether to get every individual post or weekly digests (nice but not mandatory)

Thanks in advance for your replies,
Ken