HI
My SMTP failed over to use the secondary SMTP server. I was unaware this happened. Our secondary SMTP server is in a remote location and is not as fast as our primary. I suspect most of your users have very similar SMTP configurations.
It appears that once SMTP switches over to the secondary - it does not switch back if the primary comes back online. A restart is required.
So, it would be great if SDP could send a notification to the admin if it switches from the primary SMTP to secondary.