Mandrill Webhook
Mautic supports a few of Mandrill's webhooks for bounces.
Login to your Mandrill account and go to Settings -> Webhooks
Click Add a Webhook
Mautic 1.2.2 supports the following webhooks: Message is Bounced, Message is Soft-Bounced, Message is Rejected. As of 1.2.3, Message is Marked as Spam and Message Recipient Unsubscribes will be supported.
Fill in the Post To Url as http://your-mautic.com/mailer/mandrill/callback then click Create Webhook.
Click Custom Metadata and create two new metadata fields: hashId and leadId