Feat: Simpler email connector for emails to self

Mail servers usually don't require account details for delivering to mailboxes that they "own", so a lot of the Email connector stuff could be simplified / secured more.

I.e., if an agent needs to email you, it only needs your email address: it can look up the MX record, connect to it over SMTP, and directly give it the email: no login details required. Logins are more about reading email, or proving to a server that it should queue emails to be sent ANYWHERE on the original sender's behalf.

So, a lot of the required fields in the Email Connector could probably be removed, and the "default email address" converted to a "fixed email address" for that simple (and probably much more common) case: I don't like the idea of giving current local models the ability to email any address, personally, as they're still quite error prone.

I think this would help with security of email too, since allowing SMTP auth usually means enabling SMTP service, disabling MFA on email accounts, and things like that.

Start by locating the Email Connector implementation and its configuration fields. Read how the current default email address, SMTP authentication, and outbound recipient restrictions are handled, then review the connector's tests or integration entry points. Done means the proposed self-delivery flow and fixed-recipient security model are defined and covered without removing needed functionality.