delphi spirit, forever

function IsValidEmail(const Value: string): boolean;
 
function CheckAllowed(const s: string): boolean;
var
i: integer;
begin
Result:= false;
for i:= 1 to Length(s) do
begin
// illegal char in s -> no valid address
if not (s[i] in ['a'..'z','A'..'Z','0'..'9','_','-','.']) then
Exit;
end;
Result:= true;
end;
 
var
i: integer;
namePart, serverPart: string;
begin // of IsValidEmail
Result:= false;
i:= Pos('@', Value);
if (i = 0) or (pos('..', Value) > 0) then
Exit;
namePart:= Copy(Value, 1, i - 1);
serverPart:= Copy(Value, i + 1, Length(Value));
if (Length(namePart) = 0)         // @ or name missing
or ((Length(serverPart) < 4))   // name or server missing or
then Exit;                      // too short
i:= Pos('.', serverPart);
// must have dot and at least 3 places from end
if (i < 2) or (i > (Length(serverPart) - 2)) then
Exit;
Result:= CheckAllowed(namePart) and CheckAllowed(serverPart);
end;