Are SMTP servers generally obliged to copy MAIL FROM from client-server session?

Are SMTP servers during (STMP) server-to-(SMTP) server communication generally obliged to copy MAIL FROM from client-server session? I've explicitly checked that servers of some mail providers actually exhibit this behaviour, but it doesn't seem to be a requirement enforced by https://datatracker.ietf.org/doc/html/rfc5321 . Also, I don't know how popular this practice is (if it is not a standard).

Update to be more specific: I'm primarily interested in case of a very usual e-mail message, person - to - person, domains on two different servers.

The servers are obliged to keep the return path open, the easiest way to do this is to copy the original MAIL FROM: address and re-use it in the outgoing SMTP transmission, but this is not the only way to satisfy that requirement.

Generally they do do that, but some servers take other actions such as deploying BATV, SRS or some other form of VERP.

As such it is safe to expect an email addressed to the purported sender to reach the entity responsible for creating the message, but possibly via one or more intermediaries who restore the previous SMTP sender address

The RFC 5321, 3.3 tells what the MAIL FROM:<reverse-path> is for:

The <reverse-path> portion of the first or only argument contains the source mailbox (between "<" and ">" brackets), which can be used to report errors (see Section 4.2 for a discussion of error reporting).

The originator fields in the Internet Message Format headers (RFC 5322, 3.6.2) have more specific purposes to distinguish the author (From:) from the agent responsible for the actual transmission of the message (Sender):

For example, if a secretary were to send a message for another person, the mailbox of the secretary would appear in the "Sender:" field and the mailbox of the actual author would appear in the "From:" field.

The RFC 5321 envelope sender has merely a technical purpose. It is typical in mail forwarding and mailing list scenarios to rewrite the MAIL FROM to match the forwarding domain/server or the mailing list operator. This has two benefits:

• The error reports will get back to the mailing list operator who should take care of removing erroneous addresses from the list.
• Rewriting the envelope sender does not break the SPF policy of the original domain (Shevek (2004): The Sender Rewriting Scheme).

On the other hand, such practices are slightly against RFC 5321, 3.7.5:

3.7.5. Envelopes in Gatewaying

Similarly, when forwarding a message from another environment into the Internet, the gateway SHOULD set the envelope return path in accordance with an error message return address, if supplied by the foreign environment. If the foreign environment has no equivalent concept, the gateway must select and use a best approximation, with the message originator's address as the default of last resort.

I do not see this as a problem, because the SMTP protocol has not been updated (except for the SMTP 521 and 556 Reply Codes, RFC 7504) since 2008, but the practices including email forgery prevention have evolved since.