JavaScript Validate Email using RegEx

Use the code below with an asp.net custom validator to check if an email is valid.
The code below check for a value if no value is provided then is not a valid email.

The pattern below will work with gmail's email address with "+" such as johnsmith+test@gmail.com

function ValidateEmail(sender, args)
{
   if(args.Value.trim().length > 0)
   {
       var ex = /^([a-zA-Z0-9_.+-])+@([a-zA-Z0-9_.-])+\.([a-zA-Z])+([a-zA-Z])+/;
       var re = new RegExp(ex );
       
       if(re.exec(args.Value))
       {
           args.IsValid = true;
       }
       else
       {
           args.IsValid = false;
       }
      
   }
   else
   {
       args.IsValid = false;
   }
}