LinuxQuestions.org - How to personalize email

Hi,
One of my friend asked me how to send personalized email to his clients. He uses outlook express and send email with stationery to his clients. His clients email addresses are grouped into small group. For example, eastern group has all the email addresses of clients in eastern state and so on. So when he sends email to eastern group, all the clients in eastern state receive the emails, but they all can see whoelse receive that email as well, in Cc list. What my friend wants to do is he wants to be able to send email to group, but each receiver can only see its own address in To: field, so receiver thinks that email is just for him. I tried ezmlm for mailing list. But receiver can not see his own email address in To: field, instead mailing list address. Anyone knows how to work around with that or what program is best for that case. Also webmail can be used for stationary?
With many thanks