I have the regex `^[A-Za-z]{2}[A-Za-z0-9]{9}$` to validate the format of a string **AB987654321**

```
if (!( $address -match "^[A-Za-z]{2}[A-Za-z0-9]{9}$"))

    {
     write-host $address
    }

```

I would like to modify this regex so that I would be able to validate **smtp:AB987654321@domain.com**

So the string should start with **smtp:** or **SMTP:**  

Then the above format **'^[A-Za-z]{2}[A-Za-z0-9]{9}$'**  

anything after **@**

Could someone please help?