From: mailop <[email protected]> on behalf of Paul Smith* via mailop <[email protected]> Date: Wednesday, June 18, 2025 at 2:47 AM To: [email protected] <[email protected]> Subject: Re: [mailop] Outlook.com: intermittent DKIM failure
Microsoft have decided, in their wisdom, that large senders to them have to match DKIM *and* SPF *and* DMARC. As long as lots of people choose to use Microsoft for their email, everyone else will have to meet their arbitrary terms. https://support.microsoft.com/en-gb/topic/fix-ndr-error-550-5-7-515-in-outlook-com-34cfe8f8-6fbf-457e-9e8b-9e4dbaf4e0ef It would be great if someone from the Outlook.com team on the list could speak to this. This will effectively prevent any users of their services from using our mailing list services, or from receiving mail for our domain generated by mass mailers (we very intentionally use DKIM signing for mass mailers but do *not* include them in our SPF record). Absent some adjustment from Microsoft, we’ll likely have to put out a statement indicating we’re unable to conduct business with users who use an Outlook.com/Hormail.com/etc. address.
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