> A list I am subscribed to has recently experienced a problem which some of
> my lists have come across as well: that is, mail to a user bounces and
> gets returned to the list (ie, to the To: line, and not From: or
> Sender:).
Just to clear up a common misconception...
Mail should ALWAYS be bounced to the "envelope return address". In
SMTP this is the address in the MAIL FROM command, or if a message is
not being transferred by SMTP, it is the address in the Return-Path
header field.
Mail should NEVER be bounced to an address in any header field other
than Return-Path. So bouncing to the From, Sender, or Errors-To
fields are all illegal, and mailers that do this are broken.
(See RFC 821 and RFC 1123.)
> Needless to say, this usually only happens to people subscribed to the
> digest version, so a 20 or 30k file gets sent to everyone (including those
> subscribed to individual msgs) and, if the list maintainer isn't around,
> say over the weekend, the bounced digest gets included in the next digest
> and ... well, you get the idea.
>
> Any references to just how bounced mail should be handled? I did a keyword
> search at the Internic, but just don't have time to sort thru all the
> responses it got me (besides, I already know how to unsub the offenders:-}).
Make sure the offenders (and their postmasters) know why they're being
unsubbed, so that they at least have the chance of fixing the problem.
Any mailer that exhibits the behavior you described is so badly broken
that you should consider deleting any list member who uses it. I
recently deleted every user on every list I had that used one
particular Internet gateway to Lotus Notes, for reasons very similar
to those you cite. Mailers that bounce to the From or Sender header
are bad enough -- a mailer that bounces to the To or CC header is
inexcusable, and a sure invitation to disaster.
Some mailing list manager programs try to notice when messages are
bounced back to the list, with varying degrees of success. Sometimes
they don't filter well enough, and sometimes they filter out perfectly
valid messages. Bounce message formats change over time, so an MLM
that is good at filtering today may not be so good tomorrow. (Bounce
messages are being standardized by the IETF, so this situation may
improve in a few years as the new standards start to be implemented.)
For the specific case of a digest, you might consider having the From
header field be the digest submission address, and the To: field
being an unreplyable group address...
From: foo-digest@j.random.host
To: foo-digest-members:;
...but you'll still want some filtering because of all of the broken
systems that bounce to the From header address. (Note that while it
is reasonable for a digest list to set the From header, ordinary lists
should leave the From header alone.)
Keith Moore
References:
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