Mailing List SIMS@mail.stalker.com Message #15048
From: Bill Cole <listbill@scconsult.com>
Subject: Re: why no envelope headers in e-mail?
Date: Mon, 20 Jun 2005 10:33:23 -0400
To: SIMS Discussions <SIMS@mail.stalker.com>
At 10:21 AM -0400 6/20/05, Stefan Jeglinski  imposed structure on a stream of electrons, yielding:
The only way SIMS can deliver is when it gets a legit envelope address, no? In Eudora, there is a header called x-envelope I can turn on, but no envelope header appears in received e-mail that I can tell.

That's not actually Eudora creating that header, but rather Eudora hiding it if you have it set to hide it. Some MTA's will add that header.

To clarify, I had indeed removed it from the hidden headers, thus keeping Eudora from hiding it. As I read your answer, it would then appear only if the MTA added it to begin with.

Right. And that is rare.

That hints at why there is no standard way to record the envelope recipient: there can be more than one. Back before spammers made it useful to shun such mail and before AOL established mystery bounces as a de facto standard, a lot of mail for mailing lists was delivered as one copy per domain with multiple envelope recipients (i.e. RCPT commands in SMTP) to save on bandwidth and delivery time. This is still sometimes used today but is less common than it used to be because of the degraded trust and reliability of the mail system brought on by both conscious abusers (spammers) and by shoddy mail system design and implementation (e.g. AOL, until the past couple of years.) SIMS puts a 'for' clause into its Received header when there is a single envelope recipient, but in the rare cases where there are multiple recipients it does not do so as a privacy protection.

So with SIMS, if I see a "for" in the Received header, I know there was but one envelope recipient (which is also shown). Got it. How common is this particular behavior in MTAs? Put another way, is the use of "envelope" as a separate header deprecated or uncommon now?

It has never been particularly common. The 'X-' prefix on a header is an indication that the header is experimental and not part of the mail standard or even a formally defined extension to the standard.

How about the insertion of "for"?

Received headers have traditionally been very loosely defined, but many MTA's will by default act just like SIMS: one RCPT results in a 'for' clause in the Received header.


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Bill Cole                                  bill@scconsult.com

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