None

No authentication.

TLS

Advertise STARTTLS. Requires availability of a server certificate to offer TLS.

Integrated

NTLM and Kerberos (Integrated Windows authentication).

BasicAuth

Basic authentication. Requires an authenticated logon.

BasicAuthRequireTLS

Basic authentication over TLS. Requires a server certificate.

ExchangeServer

Exchange Server authentication (Generic Security Services application programming interface (GSSAPI) and Mutual GSSAPI).

ExternalAuthoritative

The connection is considered externally secured by using a security mechanism that's external to Exchange. The connection may be an Internet Protocol security (IPsec) association or a virtual private network (VPN). Alternatively, the servers may reside in a trusted physically controlled network. The ExternalAuthoritative authentication method requires the ExchangeServers permission group. This combination of authentication method and security group permits the resolution of anonymous sender email addresses for messages that are received through this connector.