First, there are a plethora of CPAN modules to accomplish the mailing out a newsletter part. I have been using mime::lite for a couple years now and can highly recommend it.

One thing that troubles me about your question is the statement that your client wishes you to collect the addresses...from where? Do you intend to harvest addresses from the web or another online source and send your mailings out unsolicited?

If that is what you are being requested to do, I would encourage you to reject the job.

Not only is sending unsolicited mailings to end users who have not knowingly and willingly established a business relationship with your client considered a serious breach of Internet etiquette, it violates the terms of services of most ISP's and could result in you or your client loosing their service.