Outlook Express Won't Send

Here we have 5 systems in our network. Each is a Dell or Acer running Windows XP Home or Pro. All systems receive and send email thru Outlook Express and access the same email address. She and I are both v 6.00.2900.5512. For several years I have sent emails to multiple eddresses with our eddress in the "To:" line and all the clients' eddresses in the "Bcc:" line. Recently I passed that task on to another in our network. I showed her how to place our eddress in the "To:" line and all the clients' eddresses in the "Bcc:" line, just like I have been doing all this time. When she clicked send, a message window popped up saying the message could not be sent because the recipient was not in her address book. The bulk of my recipients are not in my address book either but my messages always sent just fine. Her system will send the messages individually without the recipient in her address book. When we put a couple client eddresses in her address book, then put those eddresses in the "Bcc:" line, the email sent successfully. What do you spose we are doing wrong? All ideas, suggestions, and comments will be greatly appreciated. Thanks, K.

 

Thanks DavidDG, I appreciate your taking time to consider and respond to my post. K.