I’ve found MailPress to be an excellent WordPress plugin for managing newsletters and mailing lists. The developers also offer quick support through a Google User Group.

There are a number of plugins which are very useful, such as the one that enables you to track what happens to your emails after they are sent (e.g. who opened them and when).

I have only had success sending using the addon for Sendmail, as my server does not support the fsocket function used by MailPress on default settings.

You can add users in bulk and can also import one by one.

One feature I really like is the fact that you can easily add a subscription form using shortcodes in your posts or pages.

If it is a wordpress page use shortcode
[mailpress mailinglist='xx']

where xx is the mailinglist id

How to find the id of a mailinglist ?
Under Mails > Mailinglists hover the mouse on the requested mailinglist name and see in browser status bar the url ending like …&id=xx

All in all this is a really great plugin and I’m looking forward to new versions in the future.