What is the best Separator to Separate Multiple Emails?

Question

I am using mailto link to populate bcc of users default email program.

$mem_email=" ";    
$sql="SELECT email_address FROM employee";
$contacts = $db->query($sql);
while($contact = $db->fetchByAssoc($contacts))
{
    if($contact['email_address']!="" && $contact['email_address']!=NULL)
    {
        $mem_email.=$contact['email_address'].", ";
    }
}

header("Location: mailto:?bcc={$mem_email}"); 

What is the best separator to separate multiple emails in bcc field: , or ; ?

In my case, I am using ,.

Answer 1

The separator should be a comma (,) and there should not be a space.

See RFC 6068.