// s = mail address or gmail handle
static S gmailGetHandle(S s) {
  int i = s.indexOf('@');
  if (i < 0) ret s.toLowerCase();
  S a = s.substring(0, i), b = s.substring(i+1);
  if (eqicOneOf(b, "gmail.com", "googlemail.com"))
    ret a.toLowerCase();
  fail("Not a gmail address: " + s);
}