Need expert help with C# default function parameter

I am definitely seeking some expert level C# help from an expert. I am working with some C# code that appears to use named and optional arguments. Below is a very simple example of what I am talking about. The class and function are defined on lines 1 through 4 below.

Now look at line  103 below. When I read this I am interpreting it as sending an email message which is forcing the email address to be equal to the value of "CustomRelations@ourcustomsite.com".

So am I interpreting this correctly? Will line 103 always send a default email address named "CustomRelations@ourcustomsite.com"?

If not then how can I force it to always send the email address CustomRelations@ourcustomsite.com at line 103 below?

1   class TheMail
2  {
3 public bool SendCustomEmail(Id, bool OverrideFromAddress, string fromAddress = "")
4  }

100 public void SendAMessage()
101 {
102  MyMail = new TheMail();
103   MyMail.SendCustomEmail(Id, OverrideFromAddress : true, string fromAddress : "CustomRelations@ourcustomsite.com")
104}


 
100 public void SendAMessage()
101 {
102  MyMail = new TheMail();

103   MyMail.SendCustomEmail(Id, OverrideFromAddress : true, string fromAddress : "CustomRelations@ourcustomsite.com")

104}