Exchange Online Email delivery Needs an admin

5.7.57: client was not authenticated to send anonymous mail

Likely causes

• Wrong username or password in the device or app settings.
• The device can't negotiate TLS 1.2 or later, which is needed to authenticate.
• SMTP AUTH is turned off for the mailbox or the organization.
• Security defaults are on, and Basic authentication for SMTP AUTH isn't compatible with them.
• Wrong port: 465 means the device doesn't support the required TLS.

How to fix it

1. In the device or app, check the server is smtp.office365.com, port 587, with STARTTLS or TLS turned on, and the username and password are for a licensed mailbox.
2. If the device only offers port 465 or can’t do TLS 1.2, it can’t use this method. Update its firmware or use another method.
3. Admins: check SMTP AUTH for that mailbox in Users > Active users > Mail > Manage email apps > Authenticated SMTP, or with Get-CASMailbox -Identity user@domain | Format-List SmtpClientAuthenticationDisabled.
4. Microsoft is retiring Basic authentication for SMTP AUTH. Prefer OAuth if the device supports it, or move to SMTP relay with a connector, High Volume Email (internal recipients only), or Azure Communication Services Email.
5. Don’t turn off security defaults or MFA to make an old device work. Change how the device sends instead.

Checked against: learn.microsoft.com, learn.microsoft.com, learn.microsoft.com, learn.microsoft.com