string[,] corporate = {
    {"Robert", "Bavin"}, {"Simon", "Bright"},
    {"Kim", "Sinclair"}, {"Aashrita", "Kamath"},
    {"Sarah", "Delucchi"}, {"Sinan", "Ali"}
};

string[,] external = {
    {"Vinnie", "Ashton"}, {"Cody", "Dysart"},
    {"Shay", "Lawrence"}, {"Daren", "Valdes"}
};

const string external_domain = "hayworth.com";
const string internal_domain = "contoso.com";

for (int i = 0; i < corporate.GetLength(0); i++) {
    display_email(corporate[i, 0], corporate[i, 1], internal_domain);
}

for (int i = 0; i < external.GetLength(0); i++) {
    display_email(external[i, 0], external[i, 1], external_domain);
}

void display_email(string first, string last, string domain=internal_domain) {
    string username = first.Substring(0, 2) + last;
    username = username.ToLower();
    Console.WriteLine($"{username}@{domain}");
}