fcl-md: func IsValidEmail is too weak

markdown.utils.pas

function IsValidEmail(const S : String) : boolean;

type
  TState = (sNeutral,sUser,sHost,sDomain);

var
  lState : TState;
  c : char;

begin
  Result:=False;
  if s.CountChar('@') <> 1 then
    Exit;
  lState:=sNeutral;
  for c in s do
    Case lState of
    sNeutral:
      if c='@' then
        Exit
      else
        lState:=sUser;
    sUser:
      if c='@' then
        lState:=sHost;
    else
      if c='.' then
        lState:=sDomain
      else if c='+' then
        Exit;
    end;
  Result:=lState=sDomain;
end;

1. func detects empty username and returns False. but it don't detect empty hostname nor empty domain. these return True:

IsValidEmail('a@.a')
IsValidEmail('a@a.')

2. domain-name must have at least 2 wordchars. currently, I repeat, minimal count is 0.

3. need to detect that hostname/domain have only wordchars, not any chars.

4. for username - some punctuations are allowed too. this must be checked. supported char-set for username can be asked from good AI.

note: pls don't use RegEx for this func if you work on it, it will by slower by 1-2 orders.