Anybody ever disabled "AUTH PLAIN LOGIN" in smtp

Hi crowd,

I need to solve my vulnerability:

Vulnerability Detection Result:
The remote SMTP server accepts logins via the following cleartext authentication mechanisms over unencrypted connections:
PLAIN
LOGIN
The remote SMTP server supports the 'STARTTLS' command but isn't enforcing the use of it for the cleartext authentication mechanisms.

Already added "ANY" host to "Require TLS Negotiation Hosts/Nets" but the connection an port 25 still offers me "250-AUTH PLAIN LOGIN"

Any idea how to enforce the deny of plain auth?

Thx a lot and cheers

Marcus