I've been thinking more about Message-IDs. The way nmh,
sendmail, and Fedora configure things by default, the host
part is worthless, but I expect that's common in these
halcyon days of NAT. And on some hosts, I want the real
hostname to be masked, esp. when using a masqueraded From:
address. (It can't be masked in Received headers, but I'll
do what I can.)
"Host part" is pseudo, it's after the @ and can include most
ASCII printable characters.
So I'm thinking of generating a Message-ID based on a
MAC address. Something of the form:
pid-timestamp@md, where md is the sha1 hash of the pid,
timestamp, and MAC address. That would take care of the
worthless and unmasked host part.
And as a bonus, I could easily determine if a message with a
particular Message-ID originated from my machine.
One downside is that there's no portable way to retrieve
MAC addresses. (In other words, I would just do it on Linux
but would incorporate contributions for other platforms.)
But Message-IDs are supposed to be globally unique, so I
don't think there are other easy alternatives.
We had talked about allowing the host part to be configured
by the user (identname/idname), this seems like a good place
to include that as well.
Content-ID has a very similar format to Message-ID, it just
adds the part number. I think it should be handled the same
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