Wow, for reasons best known unto their deranged selves, the goons who foisted Offal Express upon the world hid the BCC option. Here's the relevant passage from the "help" files
To send an e-mail message
On the toolbar, click the New Mail button.

In the To and/or Cc boxes, type the e-mail name of each recipient, separating names with a comma or semicolon ( ; ).
To add e-mail names from the Address Book, click the book icon in the New Message window next to To, Cc, and Bcc, and then select names.

To use the Bcc box, click the View menu, and then select All Headers.


In the Subject box, type a message title.

Type your message, and then click the Send button on the New Message toolbar.

I hope that helps you, and I hope that using the most insecure, virus-friendly email client ever written, doesn't create too many problems for you.