What is the right format for "To" and "CC"

Welcome to the forum

the To Field requires a String Array datatype variable
Give a try at: {"FirstName.LastName@D.com"}

From docu:

Hello Peter
i’ve tried that but now new error message


so it was accepted (also as mentioned in the docu)

So lets analyse the issue further:

  • Delete the To Field, Save XAML, enter: {"FirstName.LastName@D.com"}, Save XAML

When issue still remains, downgrade to

in case a preview version was used

We assume, that VB is slected as UiPath Project programming language

Hello Again
Actually it C# based
and here is how is setup look like

When c# so you can try:
new string[]{"FirstName.LastName@D.com"};