We don't currently have a direct integration with MailChimp or other similar mass email services at this time, but you can export a portion of your account Address Book (or the entire thing) as a csv spreadsheet and then import into a service like MailChimp to send big newsletters.  

With our custom reports and tagging feature in areas like the Address Book menu on the left sidebar, you can even create tailored lists for certain types of contacts and export those smaller batches to csv to keep your various mailing lists up to date.