Mass Contact

Introduction:

The Mass Contact module started out as a modified version of the core Contact module. It allows anyone with permission to send a single message to a role or group of roles (or even to all registered users). Over time, it evolved to something more than just a basic contact module to a group of users.

Features:

Here are a list of some of the features this module has:

You can send a message to one or more groups (referred to as categories) of users, which are specified by role.
Large recipient lists may be broken up into smaller chunks.
The site administrator can control how many messages are allowed to be sent by a single person in an hour.
The message may be sent such that the recipients' e-mail addresses are hidden from each other.
The message may be sent as plain text or HTML, even specifying the input format filter to use.
The message may include one or more binary file attachments.
The site administrator may specify different texts to be placed at the beginning and/or the end of every message that is sent out.
A copy of the message may be saved as a node.
Users may opt-out, by category, of receiving mass mailings on their account settings page.

Installation:

This module is installed in a standard way. Generic instructions for how to do that can be found here: http://drupal.org/getting-started/install-contrib

Configuration and Setup:

Check and potentially modify the permissions for this module (at admin/people/permissions under the Mass Contact heading) and for the content created by it under the Node heading. (There are other modules that provide additional permission settings for content, so you will have to check for those as well.)

For the Node content, there are by default these permissions:

Create new content
Edit own content
Edit any content
Delete own content
Delete any content

Technically, no one should be allowed to create or edit any Mass Contact message. These nodes are simply copies of email messages that are or were sent out. Creating a Mass Contact message node will not send the email message to anyone. Editing one that has already been sent will not update those email messages and may lead to confusion, as the copy will no longer match what was sent. You are, of course, free to delete any of the copies on the site, understanding that it will not "un-send" the original message.

Verify that the content that is created by this module is configured and displayed the way you want it to be:

Make sure the Publishing options are set correctly (especially Published and Promoted to front page) on the content type's Edit page (at admin/structure/types/manage/mass_contact in the Publishing options fieldset).
Make sure the fields you want seen are visible and the ones you do not want seen (e.g., Headers and BCC) are hidden in the display view modes (admin/structure/types/manage/mass_contact/display).

The place where you create categories and modify the module's settings is found in the same place as core's Contact module, the Configuration section of the Administer page (admin/config/system/mass_contact).

You need to add at least one category before sending any mass e-mails, which can be done at the same location where the administrative settings are.

In order to send messages in Drupal 6, you need to enable the menu item. That is done by editing the menu item in the Navigation menu at admin/build/menu-customize/navigation (Site building -> Menus -> Navigation). This was done to mimic the behavior of the Contact module. The Drupal 7 version uses a format that is more familiar to people and has this menu item automatically enabled.

More Information:

This module works by sending a single e-mail to your mail server with the recipients' e-mail addresses in either the 'To:' or 'Bcc:' field. The mail server is then responsible for parsing out the recipients' addresses and forwarding the message along to everyone.

Here is some scaling information:

This module retrieves user ids and emails in a scaled way: no
This module sends email in a scaled way: yes, within server limits
This module keeps connections up while the long process continues: no

After you have created at least one category (see Configuration and Setup above), use yoursitename/mass_contact (e.g. www.example.com/mass_contact) to open the mass contact form and send emails. For details on all the menu items/links that are available and what they do, please see: http://drupal.org/node/760548#comment-2912412

Troubleshooting and Miscellaneous:

When breaking up a large recipient list into smaller chunks and sending the message as BCC (hiding the recipients from each other), the sender will receive a copy of the message for every group of recipients the list is broken up into. That is normal behavior and cannot be changed.
If you choose to save the messages as nodes, a node type of "mass_contact" is created after the first message is saved. In addition, a menu item labeled "Mass Contact Message" will also be created under the "Create Content" menu. If the menu item is enabled, you should disable it. If it is already disabled, you should leave it disabled. That node type is used by this module to save messages, and there is no meaning for users to create Mass Contact nodes.
If your category permissions are not showing up correctly, check your category name and make sure you don't have any stray characters or any characters that Drupal doesn't allow.
If you experience "return-path" errors when sending e-mails, you can try the Return-Path module (http://drupal.org/project/returnpath) to see if that solves your problem.