Constant Contact
Constant Contact (www.constantcontact.com) is a web based email marketing service. They offer an API which allows you to add people to your Constant Contact account remotely, from your own website.
This extension connects to your member registration form and adds new members to your Constant Contact account when someone submits the registration form. You can pass custom fields across and you can specify one of your Constant Contact Interest Categories (A.K.A. Lists) to add the registrant to. The extension will optionally notify you of successful and unsuccessful attempts. As well, the status of submissions are logged in your site's CP log, available in the Admin > Utilities panel.
In order to get this extension running with your EE site, you need to load the language and extension files onto your server. Place the language file in the appropriate language directory and place the extension file in your extensions folder.
Once that's done, activate the extension in the Extensions area of your EE control panel.
The extension needs to be configured before it can be used. You need to provide your Constant Contact username and password as well as a notification address if you choose to be notified of integration attempts.
You need to set up a custom member field to allow new registrants to opt in or out of subscribing to your CC mailing list. As long as the 'no' value of your field has the letter 'n' in it and someone chooses that option, the extension will opt the registrant out and the extension will not talk to Constant Contact.
You also need to choose one of your custom fields as the field to capture a Constant Contact Interest Category (A.K.A List). The Interest Category you allow your users to submit must match exactly with those in your Constant Contact account. So we recommend that you create a custom member field with a drop down list of your Constant Contact Interest Categories / Lists.
Once the extension is configured and the necessary fields are available for users to select in your member registration form, you should be all set.