[Mailman-Users] "Bounce action notification" emails for subscribes/unsubscribes

Stephen J. Turnbull turnbull.stephen.fw at u.tsukuba.ac.jp
Mon Sep 18 04:20:10 EDT 2017

Terry . writes:

 > Sorry for the delay in responding, and thanks for your generous
 > offer of working with my webhost and/or cPanel to solve this.  I
 > passed that offer to my webhost, but it seems they have been able
 > to sort it out with cPanel themselves.

 > I then tested lists in all 7 domains, and they all sent
 > subscribe/unsubscribe emails to me perfectly.  I then asked Jim
 > Dory (who has participated in this thread) to setup a default
 > address for his list, and it worked for him, too.


 > ==========================================
 > The issue with @mydomain.com was caused due to the setting "Discard
 > the email while your server processes it at SMTP time with an error
 > message" under cPanel>>Email>>Default Address. We've setup "Forward
 > to Email Address" to
 > catchall at mydomain.com<mailto:catchall at mydomain.com>.  As cPanel
 > support explained, this indicates that all mail that is delivered,
 > but does not have an address (like mailman-bounces@) on this server
 > will be delivered to the default account - this can potentially
 > pose the risk of the email account receiving email for accounts
 > that do not exist, something commonly seen when a domain is being
 > spoofed.  Otherwise, it will be rejected with "No such user here".
 > ==========================================

 > I’m confused by the wording of the above paragraph from the
 > webhost, but maybe they mean that the server is configured to not
 > allow emails to be sent out *from* addresses which can’t receive
 > emails, and this is to help reduce outbound spam.

The reference to "SMTP" could mean "outbound," but the context doesn't
support that.  Everything else clearly indicates "inbound".

 > So, I guess when Mailman tries to send a subscribe/unsubscribe
 > notification email out from
 > mailman-bounces at mydomain.com<mailto:mailman-bounces at mydomain.com>
 > to the list owner address, maybe the server blocks it, since that
 > mailman-bounces at mydomain.com<mailto:mailman-bounces at mydomain.com>
 > address doesn’t exist, as such.

It is possible for the remote site to ask if an address exists during
your outgoing SMTP session (the tech of this is complex, so I'm not
going into detail), and many sites will refuse to accept mail with a
non-existent envelope sender.  My guess is that it's more likely that
remote sites were discarding the mail for that reason.  Your host
would be more able to tell you about that.

 > I tested this theory using a less overkill approach, by not using
 > the "catchall" default address method, but just creating a
 > forwarder (alias) for the address
 > mailman-bounces at mydomain.com<mailto:mailman-bounces at mydomain.com>

I don't understand why you don't have this address in the first place.
Mailman uses this address as envelope sender (and sometimes From) in
order to accept failed delivery notifications (aka "bounces"), and so
automatically disable delivery from Mailman to mailboxes disabled on
the subscribed host (including non-existent addresses).  This should
be configured in the MTA (mail server) along with all of the other
Mailman-specific addresses.

It may have something to do with an upgrade or reconfiguration at the
host that went wrong somehow.

 > which redirects its mail to one of my mailboxes (even to my
 > catchall mailbox), and that seemed to work!  I don't think this is
 > to provide an address which will receive emails resulting from
 > subscribes/unsubscribes (since I don't think that process sends
 > anything *to* the mailman-bounces at ... address), but just to satisfy
 > the anti-spam requirements of the system that every sending address
 > should be able to receive email, not just bounce it.

This is why the subscription process wasn't working, except for the
fact that relying on your host's description, it seems very possible
that the filtering of non-existent "From" or envelope addresses takes
place on the receiving system.

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