Is there a wordpress listserv or email group plugin?

There are plenty of WP plugins for one-way correspondence… ie mailing lists where the owner can send out newsletters, etc. but i am looking to integrate the functionality of a listserv or email group for my WP users, where anyone in the group can address the whole group, but those outside the group cannot.

i could do this in google groups, but was hoping to integrate it w/ my club’s WP site so that i could use it in conjunction with a membership plugin to keep track of who has paid the club dues and so forth.

edit to add: i think that MailPress or especially Email Users might work (Email Users if I adjust the capabilities) but ideally the group would be able to send messages from their emails to a single address (like with google groups) and not have to log in to send a message from the admin. there is no way i am going to be able to teach all of these people how to use WP, so i want the friction to be minimal. is this possible w/ WP?

We’re currently developing this for a client. It turned out to have pretty complex needs. For example, as the group grows, the number of emails being sent becomes huge (i.e. every email response goes to hundreds of people), so we are running that part of the service through SendGrid. We want everything to run through the front end, so we had to develop that. There’s also all sorts of permissions, and automatic emails that need to have a space for configuration. Emails need to be stored in some kind of thread in an archive, so we had to work that out. We’re almost finished development, and then we have to see how it runs. We are considering turning it into a plugin/theme (it needs both components), but that would take a while to release. It’s been a very interesting project.