Definition
Legacy authentication refers to older email and client protocols that authenticate in ways that frequently bypass modern interactive MFA controls.
Why it matters for business
Older sign-in methods that often cannot enforce modern MFA challenges. Identity and Microsoft 365 decisions often turn on understanding this term clearly.
Example in an SMB context
A growing firm might encounter Legacy authentication while hardening Entra ID, reviewing Secure Score, or rolling out stronger MFA for administrators.
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