Spence covered most of your questions. To be really clear...
Customers can only receive AutoSupport via SMTP, using "autosupport.to". Note: This is a filtered destination - only important AutoSupport messages are sent.
Partners (or Customers) can receive all AutoSupport transmissions (SMTP only), using "autosupport.partner.to". (7.3.x feature)
NetApp Support can receive via the selected transport protocol, all AutoSupport messages.
- If HTTP/HTTPS is selected, then they are sent to "autosupport.support.url" - optionally via a proxy (if specified)
- If SMTP is selected, then they are sent to "autosupport.support.to"
- Note: These NetApp Support destinations are hardcoded. If you do change it, they would revert back after a reboot.
I hope that helps.