Public Class Account {

  String accountService = null;
  EmailService emailService = null;

  public setAccountEmailProviderName(accountEmailProvider){
    this.accountService =  accountEmailProvider;
  }

  public void setupAccount(){

    if (accountService == "google"){

      emailService = Class.forName('GmailEmailProvider').getInstance();
    }

    else if(accountService == "yahoo"){

      emailService = Class.forName('YahooEmailProvider').getInstance();
    }

    else {

      emailService = Class.forName('HotmailEmailProvider').getInstance();

    }

      MailInit init = new MailInit(userName, password, emailService);
  }

}

public Class MailInit{

  public void initialConfiguration(String userName, String password, EmailService emailService ){
    MailConfiguration.userName = userName;
    MailConfiguration.password = password;
    MailConfiguration.emailService = emailService;
  }
}