The problem with Basic authentication
Basic authentication repeatedly presents a username and password. Devices often store those credentials for years, making a stolen password useful far beyond one application.
OAuth uses limited, revocable tokens instead. Multi-factor authentication remains at the Microsoft sign-in boundary and an individual application can lose access without a mailbox-wide password change.
What changes for SMTP applications
SMTP AUTH can use OAuth, but many printers, NAS devices, and older applications cannot perform the browser-based authorization flow. Replacing a perfectly useful device solely for authentication support is expensive and wasteful.
A bridge such as smtpify365 gives the classic client familiar SMTP settings while handling Microsoft OAuth separately. New software should integrate modern authentication directly whenever possible.
Prepare without rushing
Inventory every device that sends mail, identify its owner and mailbox, and confirm whether it supports OAuth. Test replacements before removing existing settings.
Microsoft updates its timeline and guidance, so administrators should follow the current Exchange Online documentation rather than relying on an old deadline copied into a device manual.