Unable to send backup notification with no username/password

Dear support,

I am trying to enable the option "Send e-mail notifications about the operation state" inside the Backup settings.

I fill in the "To" and the "Server" and leave "Username" & "Password" empty (because this is not required within my network). Port is "25" and Encryption is "None".
When I use "Send test message", it says it is successful (and I receive the test email).

But when I click "OK" to save the settings, I get "Not all fileds are filled correctly"...

Why is True Image expecting something more? Is this a bug?

Thanks for your help.