Sending, receiving, and organizing email in Outlook.com
Hello
I am seeing a sudden increase in similar reports from other users in this forum as well.
Unfortunately, I cannot find any official information from Microsoft acknowledging this issue. Microsoft's published requirements for SPF, DKIM, and DMARC apply to senders sending more than 5,000 emails per day. However, based on the sudden increase in reports from the last few days, I suspect these requirements may now be affecting low-volume senders as well. This is just my observation, not something Microsoft has officially confirmed.
I helped several users with this issue yesterday in this forum. One interesting thing we noticed is that email headers may show DMARC as passing, even when the sending domain does not have a published DMARC record. We were able to identify this by checking the domain using a free tool such as https://mxtoolbox.com/.
In some cases, once the missing DMARC record was properly configured and verified, emails started coming through again. But please know that this needs to be fixed on the senders end. There’s nothing you can do as recipient.
For this reason, I strongly recommend having your senders check their SPF, DKIM, and DMARC records for the affected sending domains.
If you need help checking these records, I am happy to do so. I would just need to know the sending domain name. You do not need to share the full email address.
Note: These are non-Microsoft websites. They appear to provide useful information, but be cautious of advertisements or downloads for potentially unwanted software. You do not need to download anything to use the domain-checking tools.
Also, news article about this issue: https://www.neowin.net/news/microsoft-outlook-spf-validation-error-blocks-email-sending-and-receiving/