public class SimpleSender {

    public static void send(String smtpServer, String[] to, String[] cc, String from,
                            String subject, String body, boolean HTML, String fullFilePath) {
        SendEmail(smtpServer, to, cc, from, subject, body, HTML, fullFilePath);
    }
    public static void send(String smtpServer, String[] to, String[] cc, String from,
                            String subject, String body, boolean HTML) {
        SendEmail(smtpServer, to, cc, from, subject, body, HTML, null);
    }

    // Should I provide this overload and similar ones?
    public static void send(String smtpServer, String to, String[] cc, String from,
                            String subject, String body, boolean HTML) {
        SendEmail(smtpServer, new String[] {to}, cc, from, subject, body, HTML, null);
    }
    private static void SendEmail(String smtpServer, String[] to, String[] cc, String from, String subject, String body, boolean HTML, String fullFilePath) {
     .... Send email
    }
}

public class EmailOptions {
     private final List<String> recepients;
     private final List<String> cc;
     private final List<String> bcc;

     public void setHTML(boolean html) {
         this.html = html;
     }

     ...
}

public void sendEmail(EmailOptions email) {
    ...
}

class EmailSender{

private final String body;
private final String recipient;
private final List<String> to;
private final List<String> ccs;

public  EmailSender(EMailBuilder mailBuilder){
    this.body = mailBuilder.body;
    this.to = mailBuilder.to;
    this.recipient = mailBuilder.recipient;
    this.ccs = mailBuilder.ccs;

}
public void send(){
    //
}
public  static  class EMailBuilder{

    private final String body;
    private final String recipient;
    private final List<String> to;
    private final List<String> ccs;

    public  EMailBuilder(String body,String recipient,String to){
        this.recipient = recipient;
        this.body = body;
        this.to = new ArrayList<>();
        this.to.add(to);
        this.ccs = new ArrayList<>();

    }

    public EMailBuilder addTo(String to){
        this.to.add(to);
        return this;
    }
    public EMailBuilder addCc(String cc){
        this.ccs.add(cc);
        return this;
    }

    public EmailSender build(){
        EmailSender sender = new EmailSender(this);
        return sender;
    }

 }
}

EmailSender emailSender = new EmailSender.EMailBuilder("This is an email","me","you")
            .addTo("the Other Chap").addCc("the boss")
            .build();
  emailSender.send();

if(to.length==0){
   // invalid
   }