CREATE FUNCTION dbo.EmailIsValid (@Email varchar (100))
/*
 RETURN 1 if @Email contains a valid email address syntax, ELSE RETURN 0
*/

RETURNS BIT
AS
BEGIN
DECLARE @atpos int, @dotpos int

SET @Email = LTRIM(RTRIM(IsNull(@Email, ''))) -- remove leading and trailing blanks

IF LEN(@Email) = 0 RETURN(0) -- nothing to validate

SET @atpos = charindex('@',@Email) -- position of first (hopefully only) @

IF @atpos <= 1 OR @atpos = LEN(@Email) RETURN(0) -- @ is neither 1st or last or missing

IF CHARINDEX('@', @email, @atpos+1) > 0 RETURN(0) -- Two @s are illegal

IF CHARINDEX(' ',@Email) > 0 RETURN(0) -- Embedded blanks are illegal

SET @dotpos =  CHARINDEX('.',REVERSE(@Email)) -- location (from rear) of last dot

IF (@dotpos < 3) or (@dotpos > 4) or (LEN(@Email) - @dotpos) < @atpos RETURN (0) -- dot / 2 or 3 char, after @

RETURN(1) -- Whew !!

END
Go

function checkMail()
{
	var x = document.forms[0].email.value;
	var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
	if (filter.test(x)) alert('YES! Correct email address');
	else alert('NO! Incorrect email address');
}

/^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/

Select @isValid = case when
email like '%[a-zA-Z0-9_.-]%@%[a-zA-Z0-9_.-]%.[a-zA-Z0-9_.-][a-zA-Z0-9_.-][a-zA-Z0-9_.-]'
and email not like '%[^a-zA-Z0-9_.-@]%'
and email not like '%@%@%'
and email not like '%..%' then 1 else 0 end

return @isValid