Hi Mark & others,
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. Here is the response from my webhost:
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(a)mydomain.com<mailto:firstname.lastname@example.org>. 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".
They then provided some evidence from a log that the problem was fixed.
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.
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. (For years I’ve known that the webhost was fighting outbound spam by preventing email from being sent out from *domains* which I don’t have on that server, but maybe this even applies to the address level.) So, I guess when Mailman tries to send a subscribe/unsubscribe notification email out from mailman-bounces(a)mydomain.com<mailto:email@example.com> to the list owner address, maybe the server blocks it, since that mailman-bounces(a)mydomain.com<mailto:firstname.lastname@example.org> address doesn’t exist, as such. 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(a)mydomain.com<mailto:email@example.com> 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@... 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.
Any thoughts on this, Mark/others? Confused?
I can only imagine that the problems started recently due to some update to cPanel or other change by the webhost, because having looked through the history of my subscribe/unsubscribe email notifications, it looks as if the problems only started a few months ago, but I don’t think I’ve made relevant changes to those domains for years. (When I asked the webhost about this, they responded "Unfortunately, we cannot be sure about this. The cPanel representatives haven't mentioned about any recent changes to the Exim configuration.")
Anyway, here is a summary of my subscribe/unsubscribe notification problems that seem to have been resolved by setting the default addresses for my domains to my catchall address, instead of bouncing emails sent to non-existent addresses:
1. For some of my domains/lists I’d receive notifications as *attachments* to emails which have the subject “Bounce action notification” (as per my 1st post).
2. For some of my domains/lists I’d receive subscribe emails as *attachments*, but not receive anything for unsubscribes. (Might be the other way round sometimes.)
3. For some of my domains/lists I’d receive no subscribe or unsubscribe emails at all (as per my 3rd post).