look, unauthenticated deliveru of mail to your domain at your
webhosting server is certainly possible, as that is a local domain to
that server! (or you would simply receive no mail).
Relay via your ISP SMTP server is also certainly possible
unauthenticated because that is your ISP and you have an IP address
that is allowed relay by them (some ISP might require authentication
but that is another story).
