I'm going to focus on a small part of your query:

We would like a solution that will let us send out HTML emails and then monitor who opens them etc.

There are two ways to monitor who reads a message.

First we have read receipts. These are useless as the majority of email clients are configured to ignore them (or don't implement RFC 2289 (which is not yet a standard) in the first place), and the majority of clients which aren't flash up a (very annoying) dialog box to ask the user if they want to send the receipt. Thus, the technique gives such inaccurate results as to be useless.

Second, we have webbugs. This involves sticking an external image reference in an HTML formatted email with a unique tracking ID in the query string of the URI. Since most email clients block external images by default, and since people do read mail offline, the results are (again) inaccurate. It gets worse though, unique tracking IDs are a favoured technique of Evil Spammers (TM), so spam blocking software looks for the presence of webbugs and pushes the score of messages in which it finds them that bit closer to 'spam' (not that using HTML formatting in the first place helps in this regard). This makes webbugs worse then useless for such tracking.

In a nutshell you can't get good results and you can't get bad results without annoying your readers - so forget about tracking.

Oh, and as an aside, if you want mailing list software, I suggest Mailman (even though it isn't Perl).