On 06/17/2018 08:52 AM, Michael Hennebry via CentOS wrote: > I'm petty sure I messed up attributions, so am deleting them. > >>> I believe this is a DMARC issue. Yahoo, among other places, has set >>> their dmarc records to p=reject: > >>> So, if your mail hosting provider enforces dmarc,(gmail does) and you >>> get mail from a list that doesn't rewrite the headers, and people >>> from places like yahoo post to the list, you'll likely get some form >>> of warning about being being kicked off the mailing list every now >>> and then. The frequency depends on how often people from p=reject >>> places post, and what the settings are for bounce handling of the >>> mailing list in question. > >> This is indeed what happened. An email from yahoo.com.uk caused gmail >> to reject all the mails sent by that user because of the yahoo DMARC >> settings. > > Say it isn't so: *An* e-mail, just *one* from yahoo.com.uk > caused every gmail user to have his account disabled. > > I'd heard of the DMARC thing with mailing lists before, > but had not known it enabled single e-mails of mass destruction. I run dmarc on my mail server but only in report mode, it doesn't reject. I did it as a test (for years) and am fully convinced that dmarc is worthless for real world protection. Numerous mail lists out there are configured in such a way that dmarc gets triggered and that just isn't going to change. It's a neat idea but it's not backwards compatible with the way SMTP already works. I can not recommend its use. I do recommend mail server software update if possible to be compatible but I just can not recommend mail servers enforce dmarc. DKIM is a good thing, but dmarc breaks things too badly. Even DKIM though is of limited usefulness - it seems the spammer blacklists don't really care. Even with proper DKIM signature on a domain with correct reverse DNS set up for years, they will still add you to the spam blacklist if any other host on your subnet is identified as a spammer. So even the blacklists don't really utilize this anti-spam anti-spoof technology, which makes it kind of worthless. Using DKIM as one of several factors in spamassassin though is possibly helpful, though most spammers these days have a validating DKIM sig.