Error message when the SMTP server in SharePoint does not allow anonymous access

SharePoint configuration outgoing email server

The outgoing email server configured for Sharepoint is very simple, but it may not work properly after configuration. errors may occur when sending emails, such as the user or users have been added successfully, but there was an error in sending the e-mail message. the server may not be set up correctly to send e-mail. to verify that e-mail is configured correctly, contact your server administrator"
In fact, this is not a configuration error, but the reason why the SMTP server does not allow anonymous access. In the IIS manager, select the SMTP server and set it to allow anonymous access in the SMTP server attribute.

Error message when the SMTP server in SharePoint does not allow anonymous access