On 11/1/25 9:53 AM, Jeffrey Walton wrote:
I believe they've gotten more strict about DMARC recently, which manifests as a DKIM requirement due to the implementation of this mailing list.On Sat, Nov 1, 2025 at 1:50 AM <mike.junk.46@att.net> wrote:I've seen several folks lately questioning reduced list activity. While I'm not sure of the reasonm I've failed to post several times in the last few weeks. Mutt has given this response when I try to post: SMTP session failed: 550 Request failed; Mailbox unavailable My mail goes out via smtp.mail.yahoo.com and other emails go out with no trouble. This message is using Yahoo's web mail as suggested by mrmazda on forums.debian.net. We'll se whether this gets through.I've noticed my GMail spam folder is lighter than usual, too. It has been happening over the last month or two, since September or so (maybe earlier?). My guess is -- and it is just a guess -- major mail providers have become more strict in what they accept, and it is resulting in fewer messages in both my inbox and spam. "More strict" means they are rejecting more messages, and that could be due to DKIM, SPF and ARC header problems.
DKIM signing the mail you send to this list should help with deliverability (although this is likely not the cause of the 550 error in question).
Here's what I believe is happening: for DMARC to pass either the domain in the envelope from (used by SPF) or the domain in the DKIM header must be the same as the domain in the header from. This mailing list alters the envelope from (as it should), but does not alter the header from, so SPF alignment fails. If the original mail is not DKIM signed, DMARC alignment fails due to both DKIM and SPF not being aligned, and DMARC fails as a result. The server sending the mail is identified as not being authorized to use the header from the mail has.
The real solution to this problem is to make the mailing list also update the header from.
Large mail providers use other heuristics on top of this so not even being 100% compliant with these authentication methods guarantees that mail will be delivered, but I think this list actually benefits from these heuristics (being well established, trusted IP, authentic message contents).
A concerning possibility is that every mail being sent from this list without DKIM signing might be hurting the overall reputation of the server as a whole.
monodev