String result = "fulano@mail.com;ciclano@mail.com";
int index = result.indexOf(";");
if (index > 0) {
    result = result.substring(0, index);
}
System.out.println(result);

String result = "fulano@mail.com;ciclano@mail.com";
String[] emails = result.split(";");
result = emails[0];
System.out.println(result);