I just received an email from agora-business (the list) to my callforjudgm...@yahoo.co.uk email address warning me that I was bouncing emails, and asking me to confirm that the email was still valid. (The address still works, and I still use it to receive Agoran mail; it's just that I can no longer send from it easily, so I use a different address for sending.) That might seem strange, given that I'm receiving a lot of messages to that email address too; it's not like everything is bouncing.
The culprit is probably DMARC; Yahoo! are notorious for DMARC enforcement. DMARC bounces happen when the sender of an email specifies some rules about how the email should look (e.g. sent via a particular server, or signed with a particular key), and the email, upon being received, doesn't comply with them. In other words, someone – but not most people – is sending emails that look invalid to the recipient. I'm pretty sure that the person in question is Murphy. E's been having trouble getting messages through, and eir recent message to BAK let me see what the headers on eir emails look like (because it's currently this @alumni.bham.ac.uk email address that's subscribed to BAK). It's possible to diagnose the problem from a couple of headers on the email: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1557931409; s=zm2019; d=zoho.com; i=emurph...@zoho.com; h=To:From:Subject:Message-ID:Date:MIME-Version:Content-Type:Content-Transfer-Encoding; l=6; bh=fdkeB/A0FkbVP2k4J4pNPoeWH6vqBm9+b0C3OY87Cw8=; b=mY+jo1/fI+p3ILjXOQGQ/PsgPFmqzsl5wJUzCg7YuHVXIsT1ZFZ9HSXy1NYS95lX AhYAlfHTWZikn+OfP+ECfVFiHkmpsjDTgtnGAYKjzIKN+nVOg0HBMBGgADCGKuD0xuO 4GUSndRa9qmZ5GSLcmtSdwrqukQzr64Vrs1GQhdo= Authentication-Results: spf=none (sender IP is 145.0.1.64) smtp.mailfrom=listserver.tue.nl; alumni.bham.ac.uk; dkim=fail (signature did not verify) header.d=zoho.com;alumni.bham.ac.uk; dmarc=fail action=oreject header.from=zoho.com;compauth=fail reason=000 The "dmarc=fail" is explaining the immediate cause of what's going on here: the email claims to be from zoho.com, but could not be verified as actually coming from there. The main causal factor is the "h=" part of the DKIM-Signature line: DKIM-Signature: … h=To:From:Subject:… Translated to English, this states that the email should not be considered valid if the Subject fail was modified in transit. Of course, the Subject of the email actually was modified (by the list software, inserting the BAK:), so the message fails to verify. The cryptography behind DKIM can't detect that a message is "almost right", it's just a simple pass/fail (in particular, the recipients can't distinguish an entirely forged email from an email that's correct apart from the subject line). zoho.com's DMARC settings are to tell the recipient to reject any apparently forged message that claims to be from them (without even sending it to a spam folder). So in theory, anyone who can actually receive Murphy's emails has a non-compliant mailserver :-) I used to have a similar problem back when I posted from my yahoo.co.uk email address. There's a fairly simple workaround to it: just type the DIS:/BUS:/OFF:/BAK: part of the subject line manually, rather than letting the list software add it. If you do that, then the list software doesn't modify the email in transit, so the DKIM signature starts verifying and allows the email to go through. (Incidentally, the "DMARC failures mean your email doesn't go through /and/ bounce other people off the lists" issue is fairly well known; people warned that it would happen as soon as sites started using restrictive DMARC settings. There's no really good solution to it at the list software level, though.) -- ais523