Ever heard of mail merging?
It's when you make a database full of people's information. (In your case, e-mail addresses)
You then make a "Standard Letter" which is a document with content but space for personal information.
Once you have made both of them, You Mail Merge them together and send. :-)
Maybe you can google this aswell, or use Online Help & Online Tutorial in your Word Processing program.
(This is how bills, advertisments etc are made)

Hope it helps you,
Regards, Valency.