Unable to send email via Office365

[Ilia Shapira]

Confluence Data Center was sending email for years with Office365

Recently stopped sending

We switched to 9.4.1 with OAuth. Authorize shows "The mail server is now authorized"

Test email fails with 

An error has occurred with sending the test email:
com.atlassian.mail.MailException: javax.mail.AuthenticationFailedException: 535 5.7.3 Authentication unsuccessful [YTBP288CA0012.CANP288.PROD.OUTLOOK.COM 2025-05-06T12:28:30.554Z 08DD8C2B51A3DB4F]

MFA disabled for this user

We did try to add 

CATALINA_OPTS="-Dmail.smtp.starttls.enable=true -Dmail.smtp.ssl.protocols=TLSv1.2 ${CATALINA_OPTS}"

Confluence Mail Server Setup issue due to TLS | Confluence | Atlassian Support

[Jim Knepley - ReleaseTEAM]

Hi @Ilia Shapira 

There are two spots I am curious to look at.

When configuring the OAuth application, did the client ID and client secret get copied to the SMTP server configuration correctly? It probably was, but it's worth a look.

Does the application link reference an account with SMTP.SendAsApp permission?

There are also some M365-side settings that you can read about here.

[Marc - Devoteam]

HI @Ilia Shapira 

Googling this, it seems more an office365 issue. 

See this community post: https://community.atlassian.com/forums/Jira-questions/Outgoing-SMTP-Mail-Server-Authentication-Unsuccessful/qaq-p/1434010 

Or this MS article: https://learn.microsoft.com/en-us/answers/questions/1246224/smtp-return-535-5-7-3-authentication-unsuccessful