Acajoom, provides email marketing extensions for Joomla, has upgraded their free Acajoom News to a Joomla 1.5 Native component. I use Acajoom News on a number of my sites as it is easy import users from other sites and to to run multiple newsletters with it.

It is a major step up from the default Joomla newsletter that comes with your installation. An additional benefit is that the person sunning your newsletter doesn't have to be a Super Administrator, as with the default.

Acajoom's paid versions incorporates your own autoresponder and smart newsletter systems.