A BCC list shouldn't block an email. Perhsps you should examine that question more closely, it may be something else.
Anyway you should use a solution that customizes the email itself, I write my own so can't suggest one but I'm sure there are many on the web.
The basic concept is store your data in a database, then from your online database, get the client data: first name, last name, email.
Your email will look something like this, with "markers:"
Dear [fname] [lname],
Letter content . . . .
The program goes through each active participant in your list, substitutes out the real names where the markers are, and sends out a customized email specifically to that person. You should also be able to attach images, files, and customize the email to accept html emails with images, and it should provide an alternate plain-text version if the recipient client does not support html.
This is really the way to do it, sending mail from a regular email program with a BCC or (God forbid) CC list is for small groups and personal emails, and becomes burgeonsome very quickly.