me said:
The XFORWARD_README / "XFORWARD Command syntax" currently tersely states: - The PROTO attribute specifies the mail protocol for receiving mail from the up-stream host. This may be an SMTP or non-SMTP protocol name of up to 64 characters, or [UNAVAILABLE] when the information is unavailable. This is somewhat vague, as it does not state whether the protocol name is just something like SMTP, ESMTP, QMQP, [...] In particular, it would be handy (for logging purposes) if the UTF8SMTPS?A? set would be included in the XFORWARD PROTO field.
2014-09-30 Wietse wrote:
This is intentional. It is some string, encoded if required. At the time I did not attempt to prescribe what names might exist or come into existence.
[...]
All those names would satisfy the XFORWARD spec, but requiring such names would be a different matter. As a final data point, Postfix currently does not log the "extended with" protocol name. This information does show up in the Received: header.
The coming postfix-2.12 may be a good opportunity to enhance the information value of this attribute by switching to "WITH protocol type" IANA values, especially since such string is already assembled elsewhere in postfix. Thanks to the current documentation the change would not risk breaking backward compatibility :) Mark
