Liste de diffusion Message #15045
De: Bill Cole <>
Sujet: Re: why no envelope headers in e-mail?
Date: Sun, 19 Jun 2005 13:38:56 -0400
A: SIMS Discussions <>
At 1:02 PM -0400 6/19/05, Stefan Jeglinski  imposed structure on a stream of electrons, yielding:
Not sure the question is phrased correctly, but I have wondered about this for a while.

When an MTA makes a connection, it sends an e-mail via an envelope address, no?


 There is no necessary correlation between this envelope address and the recipient's To address.


 IOW, can end up with an e-mail in his inbox that appears to have been sent "To", even if sam doesn't exist. This is an endless source of confusion to recipients that don't know how things work. And obviously I don't quite know how it works either.

Do all MTAs necessarily transmit the envelope address for display?


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.

What really determines how an end-user can see the envelope address, if ever at all?

With SIMS, the envelope recipient will appear in the SIMS-added Received header IF the message hads only one envelope recipient.

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.

Bill Cole                        

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