SMTP in the Internet is, by definition, over IP. STD1 defined only one
required reliable ordered data stream protocol - TCP.
What is your point?
Are you saying that, in the Internet, there is some application/transport
protocols not over IP but SMTP is exclusively over IP?
Multicast _redefines_ IP (or portions of the address space thereof); it
could be argued that a service provider sells 'Internet' without selling
See STD1 for a list of "required" protocols.
Multicasting is RFC1112, one of the 'required' protocols.
In RFC 2400, the last STD1 which included information on requirement
levels, it is a "recommended", not "required" protocol.
I wonder why the information is missing in the recent STD1.