Auto-Send is the option to automatically send email found in Send Mail account setup.
BigBusiness lets you add your email account in Send Mail setup and set to Auto-Send. Messages created in BigBusiness or in Mail Notify and then be set to Ready and send.q
Ready lets you set a message as ready to send, so BigBusiness can automatically send.
Sent is automatically assigned to mail that is emailed successfully.
Skip can be automatically or manually set for mail that cannot be sent, to stop trying.