What do you use to send personalized form letters to potential JVs?

Hi,

When it comes to mailing to a whole gang of people, it's much quicker
if you can create one letter with fields where you can automatically
insert specific information for that particular recipient.

For example:

In your letter, you'd have perhaps one or two paragraphs or sentences
that let the reader know that you actually did visit their site. So, you
might want to add, "I was really impressed with the excellent information
you provide on squirrel control" somewhere near the top and perhaps
some other sentence near the end.

Plus, of course, enter the person's name:
Dear Mr. Eccles -

I know that in Word, you insert fields in your letter to make the program
auto insert these bits. Fields generally look like [[firstname]] or [[para1]].

But I don't know how to do it for mailing. Like, I don't know how to do it
with Outlook, which is my email program.

I took a stab at it once and ended up accidentally sending out about
25 letters to different emails but with the same Dear [[firstname]] [[web address]].

What are you using to do these multiple mailings using a merge letter?
If you're using Outlook or Word - any tips on how to prepare the merge
BEFORE it actually sends the messages?

Appreciate your help.

Thanks.

Sylvia