I don't think you can personalise it, at least not without a professional mailer application.
One option though, is to put "Dear Customer" or something similar in the To: field, and BCC all the genuine recipients. When the email sends, it will get bounced back as such as the address in the To field does not exist, but it will still appear to all the recipients in the BCC fields.
Outlook may not let you send the email, saying that "Dear customer" or whatever is not a valid email address. If this does happen, just add a new contact. I have tested this, and added a contact as follows:
Full Name: Nobody
Email:
[email protected]
Display As: Dear Customer
I BCC'd myself into the email, and did receive it with "Dear Customer" as the To: address.
Not perfect, but it works.