From looking at the postfix logs it appears as though the SmtpClient is not even attempting to authenticate but instead just trying to send the mail anonymously. 535 5.7.3 Authentication unsuccessful when application is ... - GitHub Read this post for more details. Select the user, and in the flyout that appears, click Mail. c# - 5.7.57 SMTP - Client was not authenticated to send … Outgoing Mail (SMTP) Server: smtp.office365.com. Beginning October 1, 2022, Microsoft will begin to disable Basic Auth in all tenants, regardless of usage. Using Microsoft/Office 365 OAUTH + EWS and Ms Graph API When you’re finished, click Save changes. The issue should be resolved now. How to Disable OneDrive for Business in … Office 365 What did you expect to happen? disable and/or enable SSL and TLS protocols
