1.5 Prerequisites/Preconditions

The SMTP AUTH Extension for SPNEGO is only invoked after an SMTP client with this extension has initiated an SMTP connection and is using the SMTP AUTH Extension [RFC2554].

It is assumed that the client knows that the server supports the SMTP AUTH Extension for SPNEGO (as opposed to the SASL to GSS-API wrapper specified in [RFC4752]) before the client determines to use this extension.