| I have 5000 people in my newsgroup and I do not want them to see in the "To" field to whome else I wrote the message.|
That's the idea of the procedure I gave you.
In TB a mass mailing (via the address book) sends every recipient a message that's only addressed to him/her, hence the options to personalize them.
When you don't care for the personalizing, you simply write an e-mail to yourself and place all intended recipients in the BCC header. This lacks elegance. Another disadvantage for this kind of mail (especially with the numbers you mention) is that lots of ISPs refuse messages with so many recipients.
The disadvantage of TB's mass mailing, a separate message for each recipient, is also its strength in this case.
However, note the user license for TB states that that you're not supposed to send unsolicited commercial email (aka spam).