Actually there is a way. You can use a 3-rd party add-in for outlook
called Easy Mail Merge. When you send a mail merge with Easy mail
merge all the recipients choose by you will have in the "To" field
only his/her address. Not only that each one will see only his address
but you can customize each name for every recipient. The program can
automatically (that is if you chose to) take first, last or full name
and address them with a greeting. It has a lot of personalization
options.

You can find it he
http://www.emailaddressmanager.com/mail_merge.html