WordPress.org

1. Make sure you have already installed WordPress 3.3 or above.
2. Unzip the MailPress package.
3. Upload the mailpress folder into wp-content/plugins.
4. Make sure the wp-content/plugins/mailpress/tmp folder is writable.
5. Log in to your WordPress admin and point your browser to "Plugins" page.
6. Activate MailPress plugin.
7. Point your browser to "Plugins > MailPress Add-ons" and activate required/desired add-ons.
8. Point your browser to "Settings > MailPress", fill and save the settings for each tab (General, (Connection to your mail server), Test, ... add-ons).
9. Once everything is installed, use the Test tab in "Settings > MailPress" to validate your settings.

Never use WordPress automatic upgrade : you will loose the content of mailpress/mp-content and mailpress/tmp folders !