From:	"Peter Moylan" <ecs-isp@2rosenthals.com>
Subject:	Re: [eCS-ISP] Trouble getting mail delivered to Office365 (outlook.com), ProofPoint, and Barracuda protected domains
Date:	Thu, 24 Apr 2025 10:18:10 +1000
To:	eCS ISP Mailing List <ecs-isp@2rosenthals.com>

On 24/04/25 03:19, Lewis G Rosenthal wrote: On a lark, I tightened the DKIM policy from none to reject, and added a 50% limiter (pct=50). To avoid duplicating the DKIM header, I have turned off the smarthost configuration, and am only sending through the firewall local to the mail server. I was going to suggest avoiding having two DKIM headers. Although the DKIM standard does allow for this possibility, we don't know much about how well DKIM checkers handle this case. Running mailing lists is always a little risky, because some receiving servers like to reject mailing list mail. Your other mail headers look pretty safe to me, though, so I doubt that this is a problem in the present case. The big problem, I suspect, is that some big mail services might be adopting a "silently reject" policy, simply discarding mail they don't like instead of returning a failure reply. My choir uses a Yahoo mail account (against my advice), and a problem we had was that messages to all members went only to some members, and we were never notified about the failures. I'm no longer on the choir organising committee, so I don't know whether they are still doing it. Your pct=50 change applies only to incoming mail, so shouldn't be relevant. However, that reminded me of a problem with outgoing mail to multiple recipients. The SMTP standard says that every mail server must be able to handle up to 100 recipients for a single message, but I've found that some servers don't respect that and that the batch size has to be limited to 50 or even further. On the other hand I suspect that that "batch" issue only arises inside your own system, so maybe it's not a problem. -- Peter Moylan peter@pmoylan.org http://www.pmoylan.org

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