do you run your own mail server on your server? if so here is a gnu program that mite help out http://www.gnu.org/software/mailman/

here is another one i have heard good things about too
http://www.greatcircle.com/majordomo/

i have never used either of them but they both my be great software

A couple of years ago I was writing a program to do just this, send out the monthly news letter for the ecommerce company I was working for. I wrote it in C and linked to libesmtp, it was a very easy task, perhaps you should look at doing something like this? The application I wrote read a file that had the content of the email and another file with a delimited list of names and email addresses it would then use substitution to replace keywords in the email and send it to the address, it took about a week to write and handled about 500K of addresses, it also worked in such a way that it didn't force too much load on server itself. I also had to mess about with sendmail to reduce the timeout value for none responsive addresses.

Failing that an easier solution could be to use mailman and create a mailing list that can only be posted too by the admin, this is a webbased frontend but the backend isn't.

HTH

Ben

Two of the most recommended List scripts are - DadaMail and PHPList .

But I had small problems with both...

DadaMail - I could not ever get installed on my server [ Perl Scares Me too Much ]. But I have heard realy-really good things about it. Try it and see if you can get it installed...

PHPList - Excellent Piece of Work... But whenever a new release is there , it is usually followed by 3-4 more releases. If you can keep up with that , then its perhaps even better than the commercial scripts available.

As far as Mailman is concerned - its what SlashDot and RedHat use to manage its own list [ so you know that its reliable ] . But , Its written in Python [ IMO ] . Its more of an email discussion list but can be hidden in one way or other to behave as an announcement list. I have the documentation but never actually needed to start a list. If you want I can pass em over to you.