When your SharePoint website has many users and you try to email to them by using the "Email Users" action, you may be having some difficulties doing so.
There is an limitation to the number of characters the "mailto"-string can contain. This is 2083 characters.
function BtnEmailClick(viewId)
{
var emails = GetSelectedUsers(viewId, "email", ";");
if (emails.length == 0)
{
alert(noUserEmailSelectedMsg);
return false;
}
emails = "mailto:" + escapeProperly(emails);
window.location = emails;
return false;
}
http://support.microsoft.com/default.aspx?scid=KB;en-us;q208427
More info : http://www.mysharepointblog.com/post/2007/10/Workaround-For-SharePoint-Group-Email-Limits.aspx