Newsletter software?

Hi List,

(resent in plain text this time)

I'm new to Linux, and this is my first post to this list...

I'm building a site that will allow subscribers to send out newsletters to
their own mailing lists. I plan to handle all the opt-in part of
subscription to the list and the creation of the email templates (mixed
format, both HTML and plaintext), I just need some software I can use to
handle the actual sending of the newsletters.
I don't need any web interface for it, I just want to be able to send it
commands via our own web pages, or by entering data into a MySQL db.

Ideally the software would be able to read data out of my db of subscribers,
fetch the needed templates and piece together any mailmerge instructions
with data from the db.

The server is running Redhat 7.2, kernel 2.4.18, with PHP 4.0.6 and MySQL
3.23.41

Would anyone happen to know of any software like that?

Thanks for any help,
Dan Searle.