[tomek@vz]

Organizations still using default Microsoft 365 email domains face severe throttling starting this October. The restrictions target the onmicrosoft.com domain that Microsoft 365 automatically assigns to new tenants, limiting external messages to 100 recipients per day starting October 15. Microsoft blames spammers who exploit new tenants for quick spam bursts before detection. Affected organizations must acquire custom domains and update primary SMTP addresses across all mailboxes -- a process that requires credential updates across devices and applications.