iOS 正则格式判断邮箱失败

//利用正则表达式验证邮箱
+ (BOOL)isValidateEmail:(NSString *)email{

    NSString *emailRegex = @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}";    NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex];
    return  [emailTest evaluateWithObject:email];
}查了很多资料  都是用正则判断的  怎么我的老是验证失败