If you're using Drupal or Magento, you can install these third-party plugins/modules to route your site's mail through Mandrill.
A third-party plugin is available from ebizmarts to sync your Mailchimp marketing lists with Magento, and now integrate your Mandrill account for Magento's transactional needs, such as order status emails: Ebizmarts MageMonkey Mailchimp plugin.
A third-party extension that allows your Joomla! installation to send emails through Mandrill: http://extensions.joomla.org/extensions/content-sharing/mailing-a-distribution-lists/20624
A third-party plugin, Mailshot, offers SMTP or Mandrill integration.
The WordPress plugin for Mandrill is no longer supported.
- Mandrill does not create or maintain third-party plugins and we can't guarantee these services or products.
Before you can send email through your account, you must add SPF and DKIM records and verify ownership of your sending domains. Mandrill will not send any emails from unverified domains or domains without valid SPF and DKIM records, including public domains like gmail.com, yahoo.com, and more.
If a message is rejected and the reject reason is "unsigned" that means that the sending domain is not properly set up, and that your account cannot send and authenticate emails from that domain.