MC1117814 — Microsoft Viva Engage | Email sender domain migration from @yammer.com to @engage.mail.microsoft

Microsoft Viva Engage is updating its email sender domains from @yammer.com to @engage.mail.microsoft, starting September 2025 with completion by Q1 2026. A coexistence period will allow both domains. Admins should update rules referencing the old domains; no compliance issues identified.