Microsoft 365 is phasing out basic authentication for sending email – Synchroteam

Microsoft is gradually phasing out basic authentication (sign-in with a username and password) for sending email through Microsoft 365. We are sharing the confirmed dates in clear terms, precisely defining the systems affected, and — most importantly — assuring you that this matter has our full attention and that we will provide a solution well before the deadline.

Key dates at a glance

Through the end of December 2026 No change — existing configurations continue to work.	End of December 2026 Basic authentication disabled by default.
After December 2026 New tenants: basic authentication unavailable by default.	Second half of 2027 Microsoft will announce the final removal date.

The timeline in detail

Today → end of December 2026 We are here

For existing Exchange Online tenants, basic authentication for SMTP AUTH continues to work exactly as it does today. Nothing will stop working during this period.

End of December 2026

Microsoft disables basic authentication for SMTP AUTH by default for existing tenants. An administrator can still re-enable it temporarily, but this is a transitional solution, not a permanent option.

Tenants created after December 2026

Basic authentication is unavailable by default from the outset. OAuth (modern authentication) is the supported method.

Second half of 2027

Microsoft will announce the final removal date, after which basic authentication can no longer be re-enabled and will stop working entirely.

The point to clarify: there is not yet a single, firm date for “full shutdown.” The end of December 2026 is a disable-by-default milestone — an administrator can temporarily re-enable it — and Microsoft will confirm the actual final removal date during the second half of 2027. Our recommendation is to consider the end of December 2026 as the effective deadline, because after that date basic authentication is disabled unless explicitly re-enabled.

What is specifically affected

This change is targeted and specific. It only concerns authenticated email sending (client submission) through the Microsoft cloud using a username and password.

Affected

Exchange Online / Microsoft 365 cloud tenants
SMTP AUTH client submission using basic authentication (username + password)
The smtp.office365.com and smtp-legacy.office365.com endpoints when used with a password

Not affected

On-premises SMTP servers (including on-premises relay in a hybrid environment)
SMTP AUTH when authenticated through OAuth (modern authentication)
SMTP as a protocol — sending itself continues; only password-based sign-in is ending
Email delivery and receipt

In short: if a system sends email through smtp.office365.com (or the legacy endpoint) with a stored username and password, this is the configuration Microsoft is phasing out. The solution is to change the authentication method, not the email provider.

How Synchroteam is preparing for you

This matter has our full attention, and we are closely monitoring the steps published by Microsoft — using them to set our own internal deadlines so that a solution is ready and tested well before the December 2026 milestone.

We are tracking the dates. We monitor every update published by Microsoft and adjust our plans as soon as the schedule changes (as has already happened several times).
We are developing a “set it up and forget it” alternative so that sending email through Synchroteam no longer depends on basic authentication — without any ongoing credential management on your side.
We will support you well in advance. You will receive clear, step-by-step instructions and ample time before any change — with no last-minute rush.
No action is required from you today. Your current configuration will continue to work throughout the transition period. We will tell you exactly what to do, and when.

If you have any questions in the meantime, our team is available at support@synchroteam.com.