Confirm the current Microsoft position
Microsoft guidance and timelines change. Start with the current Exchange Online documentation rather than a date copied from an old article, device manual, or internal ticket. Basic authentication is already disabled for many Exchange Online protocols, while Microsoft publishes separate current guidance for SMTP AUTH.
Inventory every sender
Record the client, owner, location, software or firmware version, mailbox, envelope sender, internal/external recipient need, volume, attachment size, network path, and current authentication method.
- Printers and scanners
- Websites and ecommerce plugins
- NAS, backup, monitoring, and hypervisor alerts
- Line-of-business and scheduled applications
- Scripts and unattended jobs
Select a replacement method
Prefer native OAuth or direct Graph for maintained software. Consider Microsoft 365 SMTP relay when connector administration and network identity fit. Use a compatibility bridge for fixed SMTP interfaces that support STARTTLS and credentials but cannot complete OAuth.
Pilot and cut over
Choose a low-risk client, preserve rollback details, create separate credentials, test a real workflow, monitor the first days, then migrate in controlled groups. Revoke old credentials and document the new owner and recovery path.