Exchange Online has a new domain expiring soon alert, which means that a mail flow insight checks for soon-to-expire domains in the set of accepted domains for a tenant. When the insight detects a domain due to expire within 90, 60, and 30-day windows, it sends a high-severity alert to the tenant administrators to tell them that they should renew the domain(s).
https://practical365.com/exchange-online-launches-expiring-domain-insight-and-causes-a-little-confus...
