[Mailman-Users] Envelope address vs. From: header addresses

Adam Goldberg adam at agp-llc.com
Tue Jan 3 16:27:51 EST 2017


Thanks for the quick response.  From what I can see in Defaults.py in my installation of Mailman, one could 'break' Mailman the same way Kavi's ezmlm installation is broken by merely setting USE_ENVELOPE_SENDER=yes.

(excerpt from Defaults.py)
# When allowing only members to post to a mailing list, how is the sender of
# the message determined?  If this variable is set to Yes, then first the
# message's envelope sender is used, with a fallback to the sender if there is
# no envelope sender.  Set this variable to No to always use the sender.
# The envelope sender is set by the SMTP delivery and is thus less easily
# spoofed than the sender, which is typically just taken from the From: header
# and thus easily spoofed by the end-user.  However, sometimes the envelope
# sender isn't set correctly and this will manifest itself by postings being
# held for approval even if they appear to come from a list member.  If you
# are having this problem, set this variable to No, but understand that some
# spoofed messages may get through.

# Membership tests for posting purposes are usually performed by looking at a
# set of headers, passing the test if any of their values match a member of
# the list.  Headers are checked in the order given in this variable.  The
# value None means use the From_ (envelope sender) header.  Field names are
# case insensitive.
SENDER_HEADERS = ('from', None, 'reply-to', 'sender')

(And continuing the OT discussion, in a ezmlm/qmail environment, qmail passes the envelope sender address via $SENDER to ezmlm, and ezmlm uses this to check list membership.  I don't see a way in qmail/ezmlm to emulate USE_ENVELOPE_SENDER = No.  Three cheers for Mailman!)

Adam Goldberg

-----Original Message-----
From: Mailman-Users [mailto:mailman-users-bounces+adam=agp-llc.com at python.org] On Behalf Of Mark Sapiro
Sent: Tuesday, January 03, 2017 3:17 PM
To: mailman-users at python.org
Subject: Re: [Mailman-Users] Envelope address vs. From: header addresses

On 01/03/2017 11:03 AM, Adam Goldberg wrote:
> WS6 uses mailman.  I believe that mailman doesn't suffer from this problem (that is, mailman checks list membership based on the header From: address, not the envelope from address).
> Can someone verify with authority that this is the case?

When Mailman checks list membership, it tests the things listen in the installation's config (mm_cfg.py) setting for SENDER_HEADERS, the default for which is

envelope sender

in that order. If one of those contains a list member address, the first member address found is considered the poster for list membership/moderation purposes. Otherwise the post is from a non-member.

> (and OT for this list, Does anyone have any insight into why Kavi's ezmlm implementation is acting this way?  FYI, email sent via Amazon AWS SES is sent with an envelope address unique per email (it's explicitly different from the From: header address)).

Some things use envelope sender for verification as it is (or once was) considered more difficult to spoof.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan
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