Take yourself over to http://www.regexlib.com/

But you should probably heed the warning about email validation!?
http://regexadvice.com/blogs/dneimke/archive/2005/04/01/259.aspx

Jim

Hi

I think you may try to split the string with ; first , and then validate
each one.
Regex.Split Method
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/
frlrfSystemTextRegularExpressionsRegexClassSplitTopic3.asp

Best regards,

Peter Huang
Microsoft Online Partner Support

Hi you can use the following script:

if( multiEmail() )
      document.PdfEmailForm.submit();

function multiEmail()
    {
       var str=document.PdfEmailForm.to.value;
        var email = str.split(',');
        for (var i = 0; i < email.length; i++)
            {               
                if(!checkemail(email[i]))
                {
                                 alert('one or more  
                                  email addresses are not
                                  valied');   
                                return false;   
                                                    }
           
            }
                return true;   
    }

    function checkemail(email)
    {
        var str=document.PdfEmailForm.from.value;
       
        var filter=/^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/i

        if (filter.test(str) && filter.test(email))
            return (true)
        else           
            return(false)   
   
    }   

where :

document.PdfEmailForm.to.value - E-mail ids what we enter in TO field.

document.PdfEmailForm.from.value - E-mail ids what we enter in TO field.