Contacts list not all showing up in the "TO" field
 

I am having an issue sending emails to customers. Our customer email list is
in a public folder. All customers have valid email addresses. But when I sort
them by company name and select only certain companies and then click on the
"new message to contact" button, it does not pull up the complete lists. This
happen sporadically, sometimes they all show up, other times only certain
contacts show up. The list of contact is never same when this problem
happens. If I'm selecting 100 contacts, then anywhere from 20 to 100 contacts
are on the "TO" field. On the server side we are using Outlook 2003 server
and on the client side its Outlook 2000 and Windows XP. Anybody has an idea
why this is happening? Is there a limit to the number of emails addresses in
the "TO" field.

Thanks in advance.