I've had a request for a more flexible and ISP friendly newsletter solution. I looked at a bunch of open source solutions and it looks like we are going to go with phplist.

It has many features for subscribing, sending and formatting email and subscription screens.

Big plus is that it can be configured to batch and throttle large lists to fit into your ISPs email policy. ie: so many emails pr/hour, delay between emails, length of batch 'window' (how many emails pr batch over time)

Good bounce handling, admin, and its FREE!!!

Integrates very well as EZ-Pages.

Can selectively email customers based on criteria you define. (very cool)

There is a third party Zen Cart mod for this (link from phplist web site) but it seems a little buggy and it integrates so well with just EZ-Pages, no mod is really needed.

Worth checking out.