Go to Reports -> Click “New Report”

Open Accounts & Contacts -> Choose Contacts & Accounts -> Click Create

Change Date Field - Range to All Time

Click Filters - Add

Select “Last Activity” -> “not equal to” -> “LAST 30 DAYS” -> OK
https://help.salesforce.com/apex/HTViewHelpDoc?id=custom_dates.htm&language=en_US

Remove unwanted fields by dragging off and add Email field by dragging on

Save and Run Report

Click Export Details

Change file format to CSV -> Export

Create a List in Mailchimp

Go to Add subscribers -> Import subscribers

Upload CSV file -> Upload List

Import

Score!