How do I send an email to undisclosed recipients?

I have got some emails and when I have opened them it shows in to:undisclosed-recipients. How is that possible ? I mean if I were to send email to undisclosed recipients ? Can anyone tell me the process ?

I'd like to send an email to my 50 contacts but don't want everyone to know each other's email addresses. How can I do that to where it would only show "Undisclosed Recipients" under the heading "To:" ??? Please help.

I do not want to show all the recipients email addresses. How can I show in the To: column, "Undisclosed recipients" and not everyone's email addresses?

How do I send email messages using Microsoft Office Outlook to different email addresses all at the same time and just making appear in the "To" bar like it is sent to "undiscolsed recipients"?

I've been using the bcc, but I still have to list one email address before t his will work.. Friends send me emails addressed to "undisclosed recipients" on other email services.. does yahoo offer that too? If so, how does it work? Thanks

I need to send a bulk email to everyone on my list but don't want everyone to see each others emails addresses. I've received emails before and they come up with Undisclosed Recipients in the To box. Just wondering how I do this?

when i receive some emails, it says" to undisclosed recipients" how do they do that?

I want "Undisclosed Recipients" to appear in the "TO" box of my emails. Please tell me how! Thx ; )

I need to know how i can insert all my contact to BCC section rather than typing one by one please i need to learn how to do this in yahoo mail not outlook.