Book a bigger room

The mistake

Dale sends a recurring weekly calendar invite to a distribution list called 'everyone' without checking its membership, assuming it maps to internal staff. The list is actually auto-populated from every email address that has ever contacted customer support, so the invite goes out to 41,000 external customers instead of a handful of colleagues. Mailing groups and distribution lists should always be audited for membership scope before being used as a send target, especially ones with generic names.