Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Over the past three weeks I've suddenly started received spam from several subdomains in the onmicrosoft.com domain. Abuse reports don't seem to do anything since some of the reported subdomains are still actively sending spam.
I don't think I've ever seen a legitimate email from an onmicrosoft.com subdomain.
Fortunately I use Postfix so the following line in header_checks will reject all of them:
/^From:\s.*<*@*.onmicrosoft.com>/ REJECT No spam accepted